Polyurethane/Urethane Casting

Polyurethane casting uses silicone molds to produce plastic-like parts with production-quality appearance and properties for low-volume runs and functional prototypes.

Overview

Polyurethane (urethane) casting produces plastic-like parts by pouring liquid polyurethane resins into silicone molds, often under vacuum. The mold is made from a master pattern, then repeatedly filled to create short-run parts that closely mimic injection-molded plastics in look, feel, and performance. This process handles complex geometry, fine details, and smooth surfaces with minimal finishing.

Use polyurethane casting when you need 1–100+ parts with near-production appearance, but full injection mold tooling is too expensive or slow. It’s ideal for functional prototypes, pilot runs, and low-volume specialty products using rigid, flexible, or clear materials. Tradeoffs include limited mold life, moderate dimensional accuracy compared to machining, and material options that are similar to—but not identical with—production thermoplastics. For bridge production or design validation before committing to hard tooling, urethane casting offers a fast, cost-effective path.

Common Materials

  • Rigid polyurethane (Shore D)
  • Flexible polyurethane (Shore A)
  • Clear polyurethane resin
  • High-temperature polyurethane
  • UL 94 V-0 rated polyurethane

Tolerances

±0.005" to ±0.010"

Applications

  • Electronics housings and bezels
  • Automotive interior and exterior prototype parts
  • Medical device enclosures
  • Consumer product casings and handles
  • Overmold-like soft grips and bumpers
  • Short-run functional prototype assemblies

When to Choose Polyurethane/Urethane Casting

Choose polyurethane casting for low- to medium-quantity plastic-like parts that need production-grade appearance and feel without committing to hard tooling. It fits complex geometries, overmold-style designs, and functional prototypes where moderate tolerances are acceptable. It’s especially useful for bridge production and design validation before injection molding.

vs Metal Casting

Pick polyurethane casting when you need plastic-like, lightweight, or flexible parts rather than structural metal components. It gives faster turnaround, lower tooling cost, and better suitability for cosmetic prototypes, housings, and ergonomic components where metal’s strength and temperature resistance are unnecessary.

vs Injection Molding

Use polyurethane casting when quantities are too low to justify the cost and lead time of hard injection molds. It lets you validate design, material feel, and aesthetics with near-production parts and cheap tooling, then transition to injection molding once volumes and design are stable.

vs CNC Machining

Choose polyurethane casting over CNC machining when geometry is complex, includes undercuts, or mimics molded features that are expensive or impossible to machine. Casting spreads tooling cost over multiple parts, making it more economical for small batches of organic shapes, thin walls, and detailed cosmetic surfaces.

vs 3D Printing

Use polyurethane casting when you need better surface finish, more consistent mechanical properties, and production-like plastics compared to most 3D-printed materials. Once you have a good master (often 3D printed), casting lets you replicate it cost-effectively for dozens of parts with color and texture close to final production.

Design Considerations

  • Aim for uniform wall thickness where possible to reduce voids, sink, and variable shrinkage in polyurethane parts
  • Provide generous draft (1–2° or more) relative to the silicone mold parting direction to ease demolding and extend mold life
  • Avoid extremely thin walls; target ≥1.5–2.0 mm for most rigid urethanes to ensure complete fill and structural integrity
  • Add radii to internal and external corners (at least 0.5–1.0 mm) to reduce stress concentrations in the mold and in the part
  • Clearly specify material hardness, color, transparency, and any special properties (e.g., UL rating, temperature resistance) in the RFQ for accurate quoting
  • Identify critical dimensions for potential post-machining and design flat datum surfaces or simple fixturing features to control those features tightly