Polyurethane Rubber Softener — Hardness Adjustment Additive

A softener reduces cured hardness by diluting the elastomer network. That flexibility comes at a price: tear strength, tensile strength and abrasion resistance generally fall as dosage rises, and excessive loading can leave a mould that stretches out of shape or weeps additive. Softening is a controlled adjustment, not a free property change.

Softeners are matched to specific urethane systems. An additive suitable for one prepolymer chemistry can prevent full cure in another. Confirm compatible systems and the dosage window from the supplier's documentation for the grade supplied, and validate on trial castings before running production.

Where a production part consistently needs lower hardness, a purpose-formulated softer grade normally gives better mechanical properties than a hard grade diluted with softener. Softener earns its place in development work, in shops running one base system across varied jobs, and where a small hardness adjustment is needed on the bench.

Softener is dispersed fully into the specified component before the two parts are combined, batch weights are recorded so results are repeatable, and every dosage change is treated as a new specification with its own trial casting. Urethane moisture discipline still applies: containers stay sealed and additives stay dry.

Working properties are configurable options within this canonical product, not separate products. Depending on the family, that can include grade, viscosity, mix ratio, pot life and demould time, hardness, colour, particle size or fibre length, and pack format. No configuration is presented as stocked or approved until it is confirmed against the supplier's technical data for the exact material offered. Supplier grade names, factory codes and manufacturer brands are not published here.

Send the urethane system and grade you use, the current and target hardness, the part geometry and whether the parts are production or development work.