Thermoplastics, elastomers, and duroplastics: properties, similarities, and differences among plastic groups

Thermoplastics, duroplastics, and elastomers form the three material groups of polymers. They can be distinguished by their behavior when heated and their ability to return to their original shape after deformation. Thermoplastics can be repeatedly melted, but do not exhibit complete elastic return after being stressed. Duroplastics are neither fusible nor inherently resilient. Elastomers cannot be melted either; however, after being deformed, they almost completely regain their original geometry.

The different properties arise from different levels of crosslinking of the polymer chains and different glass transition temperatures. Thermoplastics consist predominantly of uncrosslinked or only weakly interconnected molecular chains that become mobile against each other under sufficient heat input. Duroplasts, on the other hand, consist of a tightly packed three-dimensional network. In elastomers, this network is significantly wider, allowing for large reversible deformations without the chains being permanently displaced against each other.

For material selection, it is simplified to state that duroplastics are suitable for rigid and permanently form-stable components, thermoplastic materials for versatile structural and molded parts, while elastomers are primarily used for sealing, damping, and compensating for dimensional and movement tolerances.

1. Thermoplastics, elastomers and duroplastics: The molecular structure determines the properties

Polymers are macromolecules composed of many thousands to several hundred thousand repeating units. In the uncharged state, the long molecular chains are not stretched; instead, they form spatially disordered knots. Both the average chain length and the distribution of chain lengths influence the material properties.

The cohesion between the polymer chains can be based on physical or chemical binding mechanisms. The physical interactions include van der Waals forces, dipole interactions, and hydrogen bonding. In addition, there are mechanical wear effects that occur when long polymer chains penetrate each other and intertwine. These physical bonds are relatively weak and temperature-dependent. As the temperature increases, the kinetic energy of the chain segments increases and the intermolecular forces decrease, causing the polymer chains to move against each other. The material softens and, at sufficient temperature, transitions into a flowable state.

Chemical cohesion, on the other hand, is created by covalent crosslinks between adjacent polymer chains. The energy of these chemical bonds is approximately one order of magnitude greater than that of physical interactions. Therefore, by supplying heat, it is not possible to break down such crosslinking points without simultaneously destroying the molecular structure. Chemically crosslinked polymers therefore do not melt but decompose at sufficiently high temperatures.

As a quantitative measure of this stability, the crosslinking density serves as the basis. This refers to the number of network nodes per specified volume of material. The so-called network length is suitable for visual description. It indicates the free-moving section of a polymer chain between two adjacent crosslinking points. The shorter these chain sections are, the denser the molecular network is and the more restricted the mobility of the chains becomes. In the case of duroplasts, the crosslinking points are located at very short distances. The dense network severely restricts the mobility of the chain segments and leads to a hard, rigid and often brittle material behavior. Elastomers, on the other hand, have a much denser network of long, mobile chain sections. These segments can expand under load and stretch strongly, while the crosslinking points prevent permanent displacement of the chains. Thermoplastics, on the other hand, do not have any permanent chemical cross-linking points. Their cohesion is based on physical interactions and mechanical slippage of the polymer chains. Upon sufficient heating, the chains become mobile and can slide past each other, resulting in the material softening and eventually melting. The differences between a fusible thermoplastic component, a brittle mold part made of phenolic resin, and a highly stretchable O-ring can thus be directly attributed to their respective molecular structure.

Thermoplastic

unconnected

Elastomer

widely interconnected

Duroplast

closely interconnected

• covalent bonding point
• Polymeric chain

Figure 1: Thermoplastics, duroplastics, and elastomers are based on long polymer chains. The number and spacing of the covalent crosslinking points significantly determine their material properties.

In addition to the degree of crosslinking, polymers are characterized by the glass transition temperature (Tg), the temperature above which the mobility of the chain segments increases significantly.

Below the glass transition temperature, molecular movements are largely frozen. The polymer is in the glassy state and behaves hard, stiff, and often brittle. Above (Tg), individual chain segments can rotate and change their spatial position. The material becomes more viscous or, provided a suitable crosslinking structure is present, exhibits rubber-elastic behavior.

The melting temperature (Tm) is different from the glass transition temperature (Tg). It occurs only in partially crystalline polymers and describes the decomposition of the ordered crystalline regions. Pure amorphous polymers do not have a clearly defined melting point. Instead, they soften within a more or less wide temperature range.

Only the interplay between the degree of crosslinking and the glass transition temperature determines the classification into the various polymer classes. Thermoplastics are chemically uncrosslinked. Whether they behave hard, brittle, tough, or flexible at a specific operating temperature depends on the location of their glass transition temperature.

Duroplasts have a tightly interconnected molecular network and are usually used well below their glass transition temperature. Elastomers, on the other hand, are much more loosely interconnected and have a glass transition temperature that is below the intended operating temperature. Both conditions must be met simultaneously. A highly loosely interconnected polymer that is used below its glass transition temperature does not behave like a rubber-like elastic material but rather like a brittle hard material.

Network density

Condition in operation

no chemical crosslinking

chemically linked

above the glass transition temperature Chain movable

unconnectedabove T_g

Part-crystalline thermoplastics

viscous to liquid at room temperature, flows under load, malleable and formable

connectedabove T_g

Elastomers

rubber elastic: large, fully reversible deformation

below the glass transition temperature Chains frozen

unconnectedbelow T_g

Amorphous thermoplastics

amorphous and glassy, rigid and brittle

connectedbelow T_g

Duroplaste

hard, brittle, stable in shape up to the decomposition temperature

Only the combination of both parameters defines the class: A highly crosslinked polymer below its glass transition temperature is not an elastomer, but a brittle, rigid material.

Figure 2: The polymer class results from the interaction between the crosslinking density and the glass transition temperature.

Polymers react to external forces and deformations via two different mechanisms. In metals, duroplasts and thermoplastics below their glass transition temperature, bond distances and valence angles are only slightly altered by external stress. Since chemical bonds resist such changes with high resistance, energy-elastic materials possess a high elastic modulus and the possible deformation path remains limited. If the bonds or the molecular structure are excessively stressed, no further reversible elongation occurs but permanent deformation results in the formation of cracks or the failure of the component.

Elastomers, on the other hand, react predominantly by entropic elasticity. Under tensile load, the originally swollen chain segments between the crosslinking points unfold and increasingly orient themselves in the direction of the load. This aligned state exhibits a higher molecular order than the disordered chain structure. This reduces the entropy of the system. After removing the external load, the polymer again strives for a state of greater disorder. The chain segments take on their swollen initial form again, and the component returns to its original shape. Elastomers therefore have a very low elastic modulus and enable exceptionally high reversible elongations.

• not chemically crosslinked
• chemically linked

Elastomers1–10 MPa

TPE5–500 MPa

Thermoplastics1,000–4,000 MPa

Duroplaste3,000–20,000 MPa

1 10 100 1.000 10.000 100.000

Elastic modulus in MPa

Figure 3: In energy-elastic materials, the restoring force is generated by the deformation of bond distances and angles. In elastomers, on the other hand, the knotted chain segments between the crosslinking points are primarily expanded.

1.1 Thermoplastics

Thermoplastics do not have permanent covalent crosslinks between their molecular chains; instead, they are bonded by intermolecular forces and the slippage of the polymer chains. Depending on the arrangement of these chains, two types of thermoplastics can be distinguished: amorphous and partially crystalline thermoplastics.

In amorphous thermoplastics such as polystyrene (PS), polycarbonate (PC), or polymethylmethacrylate (PMMA), the polymer chains are largely disordered. These materials are often transparent and exhibit a relatively uniform shrinkage behavior in different directions. Partially crystalline thermoplastics such as polyethylene (PE), polypropylene (PP), polyamide (PA), polyoxymethylene (POM), or polyetheretherketone (PEEK) contain, however, additionally ordered crystalline regions. This makes them mostly opaque and often exhibit higher resistance to chemicals. At the same time, the shrinkage is more pronounced, which increases the risk of warping in the molded part.

As the temperature increases, the mobility of the polymer chains increases, resulting in the material initially becoming soft and eventually transitioning into a melt-like, processable state. Upon cooling, thermoplastics solidify again without requiring a crosslinking reaction. This process is fundamentally reversible and can be repeated multiple times. In practice, however, thermal and oxidative damage mechanisms limit the reprocessability. High temperatures and repeated processing cycles can degrade the molecular chains, thereby reducing in particular strength, toughness, and long-term stability.

The wide range of thermoplastics available can be divided into three performance categories. Standard thermoplastics include PE, PP and PS, for example. Technical thermoplastics include PA6, PA66, POM, PBT, PC and ABS. For particularly high thermal or mechanical requirements, high-performance thermoplastics such as PPS, PEI and PEEK are available.

High-temperature plastics

up to 300 °C

• PI
• PAI
• PSU, PES
• PPSU, PEI

• PVDF
• PPS, LCP
• PEK, PEEK
• PEKEKK, PFA
• PTFE, ETFE, PCTFE

Engineering plastics

up to 150 °C

• PC
• PA 6-3-T

• PA 46, PET, PBT
• PA 66, PA 6
• PA 11, PA 12
• POM, PMP

Standard plastics

up to 100 °C

• PS, ABS, SAN
• PMMA, PPE model

• PE
• PP

Price and performance

amorphous particluar

Figure 4: Pyramid view and classification of the different plastics

Processing is mainly carried out by injection molding, extrusion, blow molding, or thermoforming. Since no chemical reaction must take place during molding, the cycle time is determined by melting, filling the mold, and cooling. Thermoplastics therefore generally allow for shorter production cycles than duroplastics and elastomers. Adhesives and production defects can be reprocessed and returned to the process with proper material separation. Additionally, thermoplastics can be welded and processed as semi-finished products by means of spot welding. Depending on the thermoplastic used, properties ranging from soft, flexible polyethylene to highly temperature-resistant PEEK compounds are achieved.

A significant constructive limitation is the creep behavior. Since there are no chemical crosslinking points between the polymers, the polymer chains can slowly shift against each other under permanently applied tension. The resulting time-dependent deformation can lead to screw connections losing their preload force, snap hooks yielding, or components changing their original geometry over very long periods of time. With increasing temperature and mechanical tension, this effect is amplified.

In the case of standard and many technical thermoplastics, the low service temperature also limits their use. The service temperature for PP and POM is typically around 100 °C, and for PA66 it is between 100 and 120 °C. Polyamide also absorbs moisture from its surroundings, which affects both its dimensions and its stiffness, strength, and toughness.

1.2 Duroplaste

Duroplasts consist of a densely packed three-dimensional network with a high density of covalent crosslinks. The freely movable chain sections between the network nodes are correspondingly short. Since duroplasts are usually used well below their glass transition temperature, they are in the hard and rigid glass state during operation.

For processing, a reactive molding compound is placed into a heated mold. There, it not only obtains its final geometry but also irreversibly forms a solid material. Molding and material formation thus take place in the same process step. This is a fundamental difference from thermoplastic molding, where a material that has already been completely polymerized is simply melted and reshaped.

After curing, a thermoplastic cannot be converted back into its original state. The finished component has no melting point and does not soften into a workable melt at increasing temperatures. If its thermal stress limit is exceeded, the polymer network instead begins to chemically decompose.

Phenolic resins (PF) are used, among other things, for commutators, switch housings, and as binders in brake pads. Epoxy resins (EP) serve, for example, as electrical potting compounds, as matrix materials for fiber-reinforced components, and as base materials for circuit boards. Unsaturated polyester resins (UP) are used in particular for SMC and BMC molding compounds, from which, among other things, headlight reflectors and technical housings are produced. Melamine resins (MF) are found in sheet materials as well as in components for electrical installations.

Typical processing methods include hot pressing, injection molding, and Duroplast injection molding. In fiber-reinforced materials, resin injection processes and prepreg technologies are also used. In industrial practice, Duroplasts are predominantly processed as filled or reinforced molding compounds. The added glass fibers, mineral fillers, or wood flour influence the stiffness, strength, shrinkage, thermal expansion, and processing behavior, and enable individual customization to the application environment. Material properties are therefore always to be attributed to the specific compound and cannot be easily transferred to the unfilled base resin.

Among the essential advantages of Duroplasts are their high stiffness and low tendency to creep. They remain largely stable in shape under a permanently applied load, even if thermoplastics would deform over time in the same environment. Phenol resin molding compounds can be used permanently at temperatures of approximately 150 to 180 °C depending on their composition. Special epoxy resin systems allow even higher application temperatures. Furthermore, Duroplasts often offer good electrical insulation properties and low flammability. Their low thermal expansion enables high dimensional stability over a wider temperature range, making them particularly interesting for electrical, thermally loaded, and dimensionally critical applications.

However, high rigidity is countered by a low deformation capability. Typical yield strains are below five percent, which is why many thermoplastics are brittle and sensitive to notches or stress peaks. Therefore, elastically deformable structural elements such as snap hooks are hardly feasible. Instead, duroplastic-compatible components require sufficiently large radii, uniform wall thicknesses, and as much as possible stress-free transitions.

Since the cured material cannot be melted, welding is not possible. Therefore, a classic recycling process through repeated melting is also excluded. However, cured Duroplast components can be crushed and used as filler to a limited extent. Connections are usually made by gluing or through mechanical joining processes. The necessary cross-linking reaction also extends the cycle time compared to the processing of thermoplastics.

1.3 Elastomers

Elastomers have a highly dense chemical network and are used above their glass transition temperature. Only the combination of these two conditions enables the rubber-elastic behavior typical of this material class. The long, mobile chain segments between the cross-linking points can stretch greatly under load and return to their disordered initial state after relief.

Unvulcanized rubber is plastic-formable and can flow under sustained stress. It is only during processing that the polymer chains are joined into a permanent network. This step, known as vulcanization, creates an elastic component from the moldable rubber mixture with restoring properties and the final properties.

In the case of synthetic rubbers such as natural rubber (NR), nitrile rubber (NBR) or styrene-butadiene rubber (SBR), crosslinking with sulfur can take place. The sulfur reacts with the double bonds of the polymer chains and forms bridges between adjacent macromolecules. The ratio of sulfur to accelerator can influence the structure of these bridges.

Conventional sulfur systems predominantly produce longer, more-atomized sulfur bridges. They often provide favorable dynamic properties and high fatigue resistance. Efficient-Vulcanization systems, or EV systems, on the other hand, form a greater proportion of shorter sulfur bridges. This can improve, in particular, the heat aging resistance and the residual compressive deformation.

Depending on the base polymer and the requirements profile, peroxidic or other crosslinking systems are also used. In a peroxidic crosslinking process, thermally stable carbon-carbon bonds are formed between the polymer chains. This process is used, among other things, in EPDM and silicone rubbers; in FKM, peroxidic or bisphenolic systems are common, depending on the type. EPDM can be crosslinked both with sulfur and peroxidic systems depending on its composition. Furthermore, silicone rubbers can be cured using addition-crosslinking systems. The crosslinking system is therefore an independent design parameter and is not solely determined by the choice of the base polymer.

A technical elastomer component is not composed solely of the polymer. The rubber mixture contains numerous other components that determine the later properties. Reinforcing and non-reinforcing fillers such as carbon black or silica affect, among other things, hardness, tensile strength, abrasion resistance and dynamic load-bearing capacity. In addition, there are plasticizers, aging inhibitors, processing aids, and the components of the respective crosslinking system. (see Additives).

For this reason, two mixtures that are both designated as „NBR 70“ can show significant differences in media resistance, residual deformation under pressure, and service life. Therefore, the indication of the polymer base and the ultimate hardness is not sufficient for a complete material specification.

Elastomer components are mainly produced by compression molding and injection molding. The choice of the appropriate process depends primarily on the quantity, component geometry, dimensions, required dimensional accuracy, and cost-effectiveness. Unlike the processing of thermoplastics, the cycle time is mainly determined by the duration of the crosslinking reaction. Vulcanization times of 3-15 minutes are therefore not uncommon, depending on component geometry and volume.

In the case of FKM, silicone and certain peroxidically crosslinked compounds, an additional heat treatment may be necessary after demolding. This post-heating process drives out volatile reaction and cleavage products and completes the crosslinking process, which is particularly important for products in the medical or food technology sectors.

To characterize elastomer materials, parameters such as hardness according to Shore A or IRHD, tensile strength, tear elongation, tear resistance, abrasion resistance, and residual compressive deformation are used. Which parameters are crucial for component design depend on the respective function. For statically pressed seals, residual compressive deformation is one of the most important individual parameters.

Elastomers perform a wide variety of functions in technical components because they can flexibly adapt to their environment, stretch and contract, seal gases and liquids, compensate for manufacturing and assembly tolerances, and decouple vibrations and body noise. Due to their high coefficients of friction, they are also suitable for gripping, transporting, and guiding tasks. Certain elastomers are also used for electrical insulation. When designing and selecting materials, the time- and environment-dependent changes in the material must be taken into account. Ozone, UV radiation, and heat cause aging processes in some elastomer blends. Other elastomers tend to swell, extract components of the mixture, or shrink upon contact with grease, oil, or fuels.

From a manufacturing perspective, elastomers differ significantly from thermoplastics. The vulcanization process leads to longer molding cycles, and a re-melting process for classic recycling is not possible. Additionally, the achievable dimensional tolerances are often higher than for thermoplastic molded parts. The required tolerance class according to DIN ISO 3302-1 is therefore ideally determined at the beginning of the design process.

1.4 Special case thermoplastic elastomers

Thermoplastic elastomers, abbreviated TPE, They combine the rubber-like flexibility with the melt-processing capabilities of thermoplastics. Unlike conventional elastomers, they do not possess a completely covalently crosslinked network. Their elastic resilience is based on a combination of soft, mobile regions and rigid material phases.

The hard phases act as physical crosslinking points at the operating temperature and prevent the soft chain segments from sliding away permanently. Upon heating, these areas lose their fixing effect, allowing the material to melt and be processed like a thermoplastic. During cooling, the physical crosslinking sites form again, and the rubber-like behavior returns.

The most important material groups include TPE-S with styrene-hard segments, thermoplastic polyurethanes (TPE-U), thermoplastic copolyesters (TPE-E), and thermoplastic vulcanized elastomers (TPE-V). TPE-V typically consists of finely dispersed, crosslinked EPDM particles in a thermoplastic PP matrix.

Since no chemical cross-linking reaction is required in the tool, TPE materials achieve similarly short cycle times as conventional thermoplastics. In many cases, burrs and cleanly separated production residues can be reprocessed. Furthermore, soft TPE components can be directly combined in multi-component injection molding with suitable thermoplastic carrier materials, eliminating the vulcanization time typical of elastomers.

These manufacturing advantages are offset by material-related limitations. At elevated temperatures, the hard phases soften, resulting in a loss of strength and resilience. The media resistance also does not reach the level of a chemically bonded elastomer. Furthermore, TPE usually shows more cracking and higher residual compressive deformation under sustained pressure. Tool costs are also usually significantly higher than those of the same component in elastomer form, as press tools are significantly cheaper than the injection molding tools required for TPE, especially for small and medium-sized batches. For dynamic-load-bearing soft components, grip surfaces, and bellows with moderate requirements, as well as sealing lips at room temperature, thermoplastic elastomers can represent a technically and economically convincing solution. In the case of static seals that are permanently pressed and at the same time exposed to elevated temperatures, chemically crosslinked elastomers are therefore usually the better choice.

2. Differences and similarities between thermoplastics, elastomers and duroplasts

For a technical comparison, the following characteristics are crucial: the meltability, the level of stiffness, and the behavior under continuous load. From these basic properties, numerous structural and manufacturing consequences can be derived – ranging from processing and joining techniques, cycle times and storage, to design and possible recycling.

Criterion	Thermoplastic	Duroplast	Elastomer
Molecular bonding	None	tightly covalent	widely covalent
Glass transition temperature (Tg)	at or above the operating temperature	about the operating temperature	at operating temperature
Behavior upon heating	softens, melts	form stable until decomposition	form stable until decomposition
Typical elastic modulus	1,000–4,000 MPa	3,000–20,000 MPa	1–10 MPa
Breaking/rupture strain	5 to over 200 %	mostly under 5 %	100–800 %
Return behavior	partially, crawling	negligible	almost completely
Creeping tendency	High	very low	slight
Durable use temperature	approx. 80–250 °C	approx. 130–200 °C	approx. 80–220 °C
Delivery form Raw material	Granulate, flowable	reactive molding compound, mat, prepreg	Unbound plasticine mass as fur or strips
Shelf life raw material	practically unlimited	limited, mostly chilled	limited, mostly chilled
Repurposed back to original	yes	no	no
Processing	Injection molding, extrusion	Presses, injection molding	Presses, injection molding
Cycle time	mostly short	medium to long	medium to long
Welding ability	yes	no	no
Recycling	Basically possible through repeated melting	not a classic recycling process, but adding it as a filler in small quantities is possible	no recycling
Achievable form-division tolerances	comparatively close	medium to tight, depending on the method and compound	comparatively far; interpretation according to DIN ISO 3302-1
Typical applications	Housing, gears, pipes and functional parts	Electrical insulated parts, brake pads and fiber composite components	Seals, bellows, suction cups and elastic bearings

In thermoplastics, forming is essentially based on a change in the thermal state: the material is melted without chemical reaction, injected into the mold, and then cooled again. In the case of duroplasts and elastomers, on the other hand, the forming process is associated with an irreversible chemical cross-linking reaction. The necessary tool-coating time therefore results from the interplay of heat input, component geometry, and reaction kinetics. The lack of fusion of cross-linked polymers results in further consequences. While thermoplastic materials can be welded by local melting, duroplasts and elastomers usually have to be bonded or mechanically joined. Engravings and splices cannot be melted again and are therefore considered to be part of the same forming process. Furthermore, duroplastic molding compounds and uncrosslinked elastomer mixtures are chemically reactive. Their shelf life is therefore limited and requires controlled or refrigerated storage.

The elastic modulus also differs significantly between elastomers on the one hand and thermoplastics or thermosets on the other. Thermoplastics and many thermoplastic components can be considered to be strain-based and approximately linearly elastic within their allowable short-term deformation range. For thermoplastics, this consideration must, however, be supplemented for permanent or increased loads by the material behavior dependent on time, temperature, and medium. For elastomers, a simple linear elastic approach is usually not suitable. Their stress-elongation curve is already significantly nonlinear at moderate deformations. Numerical simulations therefore employ hyperelastic material models. In addition, elastomers are almost completely incompressible under load. Under load, an elastomer changes its external shape significantly, whereas its volume changes only slightly. For this reason, the effective stiffness of an elastomer component depends not only on the material, but especially on its geometry and the possibilities for lateral expansion. A uniformly enclosed elastomer layer can hardly deflect under pressure and therefore has a very high apparent pressure stiffness. The same compound remains extremely flexible as a slender, laterally deformable ring.

Thermoplastics exhibit a pronounced viscoelastic creep behavior. Since no chemical net nodes are present, the polymer chains can gradually shift against each other under permanently applied tension. The deformation therefore increases with the duration of the load. In the case of duroplasts, the tightly knit network prevents any significant sliding of the polymer chains. Their creep tendency is therefore significantly lower. However, full time-independent durability is not guaranteed for duroplasts, especially not at temperatures near their glass transition or melting point. The chemical network of an elastomer also prevents the chains from flowing continuously. However, under constant deformation, the required restoring force still decreases over time. This process is referred to as stress relaxation and is particularly relevant for seals: If the pressure applied becomes too strong, the available sealing force reserve is reduced. The three material classes also differ significantly in their delivery form. Thermoplastics are predominantly supplied as flowable granules and are only melted during processing. Duroplasts, on the other hand, enter the production process as reactive molding compounds, resin systems, mats, or preimpregnated fiber blanks – so-called prepregs – and harden chemically there. Elastomers are supplied as uncrosslinked rubber compounds, usually in the form of sheets, strips, or preformed billets. They only obtain their permanent elasticity through vulcanization in the mold.

3. From function to material: thermoplastic, duroplast or elastomer?

If the component is intended to transmit forces or form a structural component, thermoplastic and duroplastic materials are particularly suitable. However, elastomers are predestined for sealing, damping, and compensating for tolerances.

Within the polymer groups, it is also necessary to take into account the temperature profile. In the range of the glass transition temperature, an elastomer loses its elastic rubber-like flexibility and becomes hard and brittle. Furthermore, when in contact with media, the combination of medium, temperature, and holding time must always be considered. EPDM, for example, is suitable for hot water, but not for mineral oil; with NBR, the reverse is true. In addition, approvals may be required for drinking water, food, or medical applications.

For permanently pressed seals, residual pressure deformation and stress relaxation are key selection criteria. High requirements can preclude TPE and determine the choice of crosslinking system for elastomers. In thermoplastic materials, however, creep is often critical, as it can lead to a loss of preload over the long term in stressed structures. Metallic sleeves in the flow of force or crack-resistant Duroplasts offer more robust solutions in this regard.

Furthermore, the planned quantity influences the manufacturing process. For small series and large components, compression molding presses are often economical due to cheaper tools. At high quantities, injection molding offers shorter cycles, better dimensional accuracy, and less rework despite higher tool costs.

Thermoplastics can generally be recycled in terms of material after sufficient purity of the raw material has been achieved. Duroplasts and crosslinked elastomers, however, cannot be melted down again. The combination of materials that are firmly bound together further complicates separation.