Expansion ratio is the degree to which polyurethane foam grows in volume from its liquid state to its cured solid, expressed as a ratio such as 15 to 1; it determines how much space a given amount of foam will fill and the lift it can generate.
In depth
As the A- and B-sides react, the mixture expands rapidly, reaching about 90% of final volume within seconds, and it is this expansion that fills voids and pushes the slab upward. A higher expansion ratio fills more space per shot; a lower ratio produces a denser, stronger foam. Reaction time works alongside it: a slower reaction lets the foam travel farther before it sets.
Matching expansion, density, and reaction time to the job is what lets a technician lift precisely, fill a large deep void, or spread far under a rocking slab.
How Acme applies it. Acme’s formulations show the trade-off clearly: RR-401 expands roughly 17 to 1 for general lifting, while the denser RR-601 expands about 12 to 1 for maximum strength on heavy loads.
Related terms: Foam Density, Compressive Strength, Polyurethane Foam, Two-Component Polymer
Frequently asked questions
Why does expansion ratio matter?
It controls how much void a shot of foam can fill and how much lift it generates. Higher expansion fills more space; lower expansion yields a denser, stronger foam.
How fast does the foam expand?
Very fast. The reaction reaches about 90% of final volume within seconds of the two components mixing at the injection point.