PU rubber is polyurethane rubber, a synthetic elastomer made by combining two chemical building blocks: isocyanates and polyols. It sits in a sweet spot between conventional rubber and rigid plastic, which is why you’ll find it in everything from forklift wheels to phone cases to industrial seals. What makes PU rubber unusual is its versatility. By tweaking the recipe, manufacturers can produce materials ranging from soft gel-like cushions to rock-hard structural components.
How PU Rubber Is Made
The chemistry behind polyurethane is a reaction between two liquid ingredients. One component contains isocyanate groups (reactive nitrogen-based molecules), and the other contains polyols (compounds with multiple hydroxyl, or alcohol, groups). When mixed, these react to form urethane linkages, which are the repeating chemical bonds that give the material its name and its elastic properties.
If both ingredients are simple two-ended molecules, the result is a linear, flexible chain. If one ingredient has three or more reactive sites, the chains cross-link into a three-dimensional network, producing a stiffer, more durable material. This is the fundamental dial that manufacturers turn to control whether the final product feels like a rubber band or a bowling ball. Additional ingredients like chain extenders, catalysts, and blowing agents (which create foam) fine-tune the result further.
Thermoset vs. Thermoplastic PU
PU rubber comes in two broad families. Thermoset polyurethane uses cross-linked chains that permanently lock into shape once cured. You can’t remelt it. This type dominates industrial applications where parts need to hold up under heavy loads and harsh conditions.
Thermoplastic polyurethane (TPU) has no cross-links. Instead, it’s a block copolymer with alternating hard and soft segments that physically entangle rather than chemically bond. Because of this, TPU can be melted and reshaped, making it compatible with injection molding and 3D printing. TPU tends to show up in consumer goods, phone cases, shoe soles, and flexible tubing where recyclability or complex shapes matter more than extreme durability.
Hardness and Physical Properties
One of PU rubber’s defining traits is the enormous range of hardness it can achieve. Hardness is measured on the Shore scale, and polyurethane spans nearly the entire range:
- Soft PU: 10 to 60 Shore A, roughly the feel of a pencil eraser or a soft gel pad
- Medium PU: 60 to 90 Shore A (or 40 to 60 Shore D), similar to a car tire or skateboard wheel
- Hard PU: 60 Shore D and above, approaching the rigidity of hard plastic
Beyond hardness, PU rubber is prized for exceptional abrasion resistance. In applications involving severe wear, polyurethane consistently outperforms metals, plastics, and conventional rubber. It also offers strong load-bearing capacity, good elasticity, and solid tear resistance. Compared to silicone rubber, polyurethane handles fuels, mineral oils, hydraulic fluids, and physical abrasion far better. Silicone, on the other hand, tolerates wider temperature extremes and resists compression set (the tendency to stay squished after prolonged pressure) more effectively.
Temperature and Chemical Resistance
PU rubber functions well across a temperature range of roughly −60°C to 140°C (−76°F to 284°F). Within that window, it maintains its flexibility in cold conditions and resists deformation in heat. Outside that range, performance drops off quickly.
Chemically, polyurethane holds up well against a long list of substances: mineral oil, castor oil, cottonseed oil, glycerin, sea water, phosphoric acid at moderate concentrations, sodium hydroxide solutions, carbon dioxide, butane, and most common hydraulic fluids. It performs reliably around fuels like reference fuel A (pure gasoline) and standard automotive oils.
Where PU rubber struggles is with strong solvents and certain aggressive chemicals. Acetone, toluene, xylene, methyl ethyl ketone, lacquer solvents, and chlorinated solvents like carbon tetrachloride and trichloroethylene will cause severe degradation or outright failure. The same goes for concentrated acids like nitric and sulfuric acid, bleach (sodium hypochlorite), chlorine gas, and boiling water. If your application involves any of these, a different elastomer is the better choice.
Common Applications
PU rubber’s combination of wear resistance, load capacity, and tuneable hardness makes it a go-to material across industries. Solid polyurethane wheels and tires are standard on forklifts, grocery carts, roller coasters, and wheelchairs, where they absorb vibration without going flat. Industrial rollers, conveyor belt components, and drive wheels rely on PU for the same reasons.
In sealing applications, microcellular polyurethane foam is used to make gaskets and seals that need to conform tightly to irregular surfaces. Automotive parts like suspension bushings, bumpers, fenders, and steering wheel covers are commonly polyurethane. Rigid PU foam serves as insulation in buildings and refrigeration, while flexible PU foam is the material inside most furniture cushions and mattresses. Electrical potting compounds, protective coatings, and carpet underlay round out the list.
How PU Parts Are Manufactured
The manufacturing method depends on the type of polyurethane and the production volume. Thermoset PU parts are often made through open casting or vacuum casting, where liquid resin is poured into a mold and allowed to cure at room temperature or with gentle heat. Vacuum casting uses silicone molds and a vacuum chamber to eliminate air bubbles, producing parts with smooth surfaces and fine detail. This method works well for prototypes and small batches.
For high-volume production, thermoplastic PU is processed through injection molding, where the material is melted and forced into a steel mold under high pressure. This is faster and more repeatable, but the tooling costs are significantly higher. Extrusion (pushing TPU through a shaped die) produces continuous profiles like tubing and film.
How It Compares to Other Rubbers
Natural rubber remains cheaper for basic applications and offers excellent elasticity, but it wears faster and degrades when exposed to oils and UV light. Silicone rubber handles temperature extremes better (from below −100°C to above 200°C) and is non-toxic, making it the standard for medical and food-contact uses. But silicone tears more easily and can’t match polyurethane’s abrasion resistance or load-bearing strength.
PU rubber fills the gap for applications that need rubber-like flexibility with plastic-like toughness. When the job involves heavy loads, repetitive friction, or exposure to oils and fuels, polyurethane is typically the most cost-effective choice. When the job requires extreme heat, prolonged compression, or contact with strong solvents, other elastomers will serve better.