What Is Urethane? Types, Properties, Uses, and Casting

Urethane is the common manufacturing name for polyurethane, a family of polymers available as flexible elastomers, rigid plastics and foams. Polyurethane rollers, seals, bushings and cast parts use different formulations, so the material name alone cannot establish hardness, tensile strength, tear resistance or service life. To choose a grade, match the load, contact surface, geometry, temperature and fluid exposure to its test results and curing condition. For bonded cast parts, check the metal interface and repeated loading separately.

1. What Is Urethane?

Polyurethane is produced by reactions involving isocyanates and hydroxyl-containing ingredients, usually polyols. Its formulation, additives and cure control whether the finished part behaves as an elastic tread or a rigid housing. You cannot assign one universal strength or hardness to all polyurethane materials.

1.1 Urethane vs. Polyurethane: What Is the Difference?

In chemistry, urethane denotes a carbamate group or compound. Polyurethane denotes polymers containing urethane linkages. In a manufacturing RFQ, cast urethane commonly means cast polyurethane; neither term specifies a grade, Shore scale or allowable component load. Two 80 Shore A cast formulations can have different tensile, tear and compression performance.

1.2 Is Urethane a Rubber or a Plastic?

Polyurethane is a polymer that can be formulated as a flexible rubber-like elastomer, a rigid solid or a cellular foam. Thermoset polyurethane forms a cured crosslinked network; thermoplastic polyurethane (TPU) softens during heat processing. Similar Shore hardness does not mean equivalent stiffness, fatigue response or chemical resistance.

2. Types of Polyurethane Materials

Polyurethane types should be compared by both processing family and finished behavior. A thermoset can be flexible; a thermoplastic can also be an elastomer. The resin families and reference ranges in our polyurethane materials and properties library support an initial grade shortlist, not a substitute for application testing.

2.1 Thermoset and Cast Polyurethane

A two-component urethane casting resin reacts after mixing and cures inside a mold. Polyurethane casting can form solid elastomer tires, pads or rigid components. Metal-core rollers add an interface requirement: primer preparation, core features and adhesion matter as much as polymer properties.

2.2 Thermoplastic Polyurethane (TPU)

TPU is melt-processable by polyurethane molding processes such as injection molding or extrusion. It belongs to the polyurethane family but cannot automatically replace a chemically cured cast urethane elastomer. Specify the grade and compare behavior at matched strain, temperature and operating conditions.

2.3 Rigid, Flexible, and Foam Polyurethane

A polyurethane elastomer handles compliant contact; rigid grades are used where stiffness matters; polyurethane foam adds cell structure and density as controlling variables. Polyether polyurethane and polyester polyurethane are chemistry families with different hydrolysis, abrasion and fluid-exposure responses. Check the named grade, not the family label.

3. Which Urethane Properties Matter for Engineered Parts?

For a urethane material specification, urethane properties such as polyurethane hardness indicate indentation response, tensile and tear tests describe defined coupon loading, and compression set describes recovery after controlled squeeze. None alone qualifies a complete wheel, seal or bonded assembly.

Test and scope	What the result means	Engineering decision and limit
ASTM D2240-15(2021), Shore A or D	Indentation hardness, with stated specimen and dwell	Use for specified hardness acceptance; do not infer fatigue or tensile strength
ASTM D412-16(2021), elastomer tensile	Strength, strain and stress at a specified extension	Compare only matched geometry, speed, conditioning and cure; not a finished wheel load rating
ASTM D624-00(2020), tear type identified	Tear load normalized by measured thickness	Use matched Die A/B/C/T/CP methods; not an interchangeable crack-growth property
ASTM D395-18(2025), A/B/C identified	Residual deformation after prescribed compression and recovery	Use for squeeze recovery; do not infer dynamic fatigue or sealing-force retention

3.1 Shore Hardness and Surface Contact

ASTM D2240-15(2021) provides the shore hardness test method for durometer indentation hardness. Shore A hardness is common for flexible elastomers; Shore D hardness is used for harder grades. The scales are not interchangeable. Conventional specimens generally require at least 6 mm thickness unless equivalence is established. Record test surface, support, measurement locations, reading time and temperature. A flat coupon may be preferable to a curved, narrow roller tread, but it cannot validate rolling fatigue.

3.2 Tensile Strength, Elongation, and Tear Resistance

ASTM D412-16(2021) measures polyurethane tensile strength and elongation of appropriate elastomers using specified specimen and strain measurements. For the common dumbbell procedure, grip separation is 500 ± 50 mm/min. Report tensile strength and elongation with the specimen method, geometry and conditioning. Stress at 100% or 300% elongation is not automatically Young’s modulus. The site’s ultimate tensile strength guide explains the broader tensile terminology but does not replace rubber-specific D412 testing.

ASTM D624-00(2020) measures tear resistance using selected specimen types. A Die C value must not be treated as interchangeable with trouser tear or as the crack-growth limit of a rotating wheel. The reported force divided by measured specimen thickness has units N/mm, numerically equal to kN/m.

3.3 Compression Set, Wear, and Environmental Exposure

ASTM D395-18(2025) defines compression-set methods using constant force (A), fixed deflection (B) or hardness-related deflection (C). For Method B, compression set is the unrecovered thickness divided by imposed compression, multiplied by 100%. Record time, temperature, gap, recovery interval and specimen geometry. It does not measure retained sealing force or cyclic rolling durability; the separate compressive stress in plastic parts guide addresses the stress concept rather than permanent recovery.

Polyurethane abrasion resistance and urethane wear behavior depend on contact pressure, sliding or rolling speed, humidity, heat, oil and solvent exposure. A harder tread may wear faster in an unsuitable friction pair. A relevant surface-wear or component-level test is more useful than a generic hardness comparison.

4. Where Is Urethane Used?

4.1 Rollers, Wheels, and Wear Parts

Urethane rollers and polyurethane rollers, like urethane wheels, put a resilient surface over a metal or polymer core. For belt guidance, specify radial load, speed, belt material, runout and adhesion. Flat spotting, rolling fatigue, local heating and delamination can govern life even when the tensile coupon passes.

4.2 Seals, Gaskets, Bushings, and Bumpers

Urethane seals and polyurethane gaskets need compatible process fluids, controlled squeeze and suitable compression recovery. Urethane bushings, polyurethane bushings and urethane bumpers face repeated deflection and heat buildup. Select a formulation with tests matched to the component’s actual movement; hardness alone does not qualify sealing or damping.

4.3 Housings, Grips, and Prototype Parts

Cast urethane parts can support enclosure fit, soft-touch grips and functional iterations without committing immediately to production tooling. Match any prototype resin to the intended performance claim. Rapid prototyping of plastic parts can establish assembly fit; it does not automatically certify long-term UV, heat or chemical resistance.

5. How Is Cast Urethane Made?

5.1 Mixing, Casting, Curing, and Post Cure

The urethane casting process starts with a named resin, specified A:B ratio, mold or insert preparation and controlled mixing. Degassing, filling, curing and any post-cure follow that formulation’s instructions. Air entrapment, moisture, poor primer preparation and off-ratio mixing can cause pores, incomplete cure or weak bonds. Polyurethane vacuum casting uses silicone molds for many prototype geometries; a reusable metal-core tool, as used in the case below, has different setup and interface controls.

5.2 Casting vs. Injection Molding

Cast urethane vs injection molding is a manufacturing-route question, not a universal volume threshold. Cast thermoset formulations suit some encapsulated cores and elastomer geometries. Rapid injection molding is appropriate for compatible melt-processable grades where tooling and quantity make economic sense. The published cast urethane automation case details a separate 250-piece tooling decision; this article focuses on material behavior and part qualification.

6. How Do You Choose the Right Urethane Material?

6.1 Match Properties to Failure Mechanisms

Start with what can stop the part working: crack propagation at an edge, flat spotting, loss of seal contact, abrasion or bond failure. Match each risk to a grade-specific property and, where appropriate, a finished-component test. A 75–85 Shore A acceptance band can control hardness consistency without proving the service life of a bonded roller.

Functional problem	Choose or test based on	Avoid this shortcut
Rolling wheel and bonded core	Contact fatigue, wear, runout, adhesion, heat	Choosing only by Shore hardness
Compressed gasket or bumper	Squeeze, D395 set, temperature, media, cycle count	Equating compression set with sealing force
Nick or sharp edge	Edge radius, local strain, D624 test geometry	Treating Die C as a service-life limit
Rigid or flexible prototype	Production material target, cure, tolerances, quantity	Assuming cast PU replicates production ABS or TPU

6.2 When Urethane Is Not the Right Material

Urethane vs rubber, polyurethane vs rubber or polyurethane vs silicone cannot be resolved with a universal winner. Chemical compatibility, prolonged heat, hydrolysis, UV exposure and the friction pair may favor another elastomer. Rigid polyurethane vs epoxy is a different comparison: the epoxy resin manufacturing guide addresses bonding and tooling uses where flexibility may not be desirable.

6.3 What to Specify for a Custom Urethane Part

An RFQ should name the commercial grade, casting and curing route, insert material, critical dimensions, hardness scale and test protocol, operating load and environment, and component-level risks. The casting DFM guidelines help locate gates, parting lines and finish allowances. Manufacturing tolerances and standards guide how to call out functional dimensions. A supplier can inspect bore and runout while separately evaluating adhesion and rolling contact.

7. Engineering Case: Cast Urethane Conveyor Guide Roller

EPOC CRAFTER engineering data describe a 60-piece batch of cast polyurethane coated guide rollers for packaging conveyor equipment, lot PU-261012-A. The unfilled two-component material is Smooth-On PMC-780 DRY, with A:B mass ratio 2:1 and a nominal 80 Shore A hardness. The guide roller contacts a polyester-fabric belt on a conditioned 45 steel core.

The roller has 80.0 mm nominal outer diameter, 40.0 mm face width, 20.0 mm bore and 50.0 mm steel-core outer diameter, giving a nominal 15.0 mm polymer ring. The process uses core cleaning, roughening, primer, an anti-rotation feature, degassing and casting. The recorded cycle is 48 h at 23 °C, followed by 6 h post-cure at 65 °C and at least 24 h at 23 °C before tests. The bore establishes the datum for final tread turning.

The operating specification calls for radial contact load up to 120 N, rolling speed at most 0.30 m/s and indoor temperature of 15–35 °C. Dimensional limits are 80.0 ± 0.3 mm outer diameter, 40.0 ± 0.3 mm width, 20.000–20.021 mm bore and radial runout at most 0.20 mm. Recorded dimensions are 80.08 mm, 40.06 mm, 20.012 mm and 0.12 mm, respectively; each meets its stated limit.

The material properties recorded for selection are 6.21 MPa tensile strength, 750% elongation at break, Die C tear strength 35.0 kN/m, and 80 Shore A nominal hardness. The product hardness criterion is 75–85 Shore A. The project compression-set limit is 25% under ASTM D395 Method B. Using 12.50 mm initial thickness, 9.375 mm compressed gap and 11.94 mm recovered thickness yields (12.50 − 11.94)/(12.50 − 9.375) × 100 = 17.92%, within the criterion. This thickness-recovery test addresses compression set, not the wheel’s dynamic bond or rolling-fatigue life.

The steel core uses rounded groove roots, controlled blast preparation and primer to reduce stress concentrations and interface risk. At the 79.7 mm minimum wheel diameter and 50.0 mm core, radial tread thickness is 14.85 mm. Dividing 120 N by the 40 mm face gives 3.0 N/mm nominal line load. The engineering decision separates dimensional conformance from rolling wear, frictional heating and bond durability under load.

8. Questions Engineers Ask About Urethane

8.1 Can Cast Urethane Replace TPU at the Same Shore Hardness?

Not on hardness alone. Cast urethane and TPU can have different stress–strain responses, manufacturing histories and compression recovery even at similar Shore A readings. Compare grade-specific modulus or stress at strain, temperature and the loaded part geometry before changing material.

8.2 What Material Works for a High-Friction Drive Wheel?

The friction pair and durability requirement decide. Urethane rubber is one candidate for drive wheels, but belt surface, normal force, sliding, temperature and wear must be evaluated together. A higher coefficient of friction on a coupon is not a guaranteed service-life improvement.

8.3 Which Elastomer Suits a Compressed Bumper or Bushing?

Specify deflection range, loading cycles, operating temperature and maximum permanent set before choosing polyurethane, TPU or another rubber. A urethane elastomer with the correct hardness can still generate unacceptable heat or retain too much deformation.

8.4 Can a Polyurethane O-Ring Serve as a Rotating Shaft Seal?

A polyurethane seal may suit some shaft interfaces, but speed, squeeze, shaft finish, contamination and particulate limits govern selection. For cleanroom or low-particle use, inspect the actual friction pair and consider alternative seal geometries rather than choosing solely by polymer name.