High Expansion Foam vs. Low Expansion Foam

Insulating expansion foam (“spray foam”) is measured by how much the liquid form of it expands once it’s dispensed out of its container (hence the terms “high expansion” and “low expansion” foam). In fact, the foam actually does most of its expanding in the nozzle, than on the surfaces or in the crevices it’s applied; and both high and low expansion foams are designed to cover large surface areas, holes and gaps.

But here’s how these two types of foam differ:

  • Low expansion foam expands 20-30 times its liquid size and is suitable for quickly filling cracks and small openings (e.g., space along the floor and wall intersection); plumbing, HVAC and electrical penetrations (e.g., gap between the hole and pipe); and large spaces such as unfinished walls, ceilings and floors in the basement, attic and crawl spaces.
  • High expansion foam, in comparison, expands 200-300 times its liquid size and is more appropriate for use in larger, commercial or industrial spaces. In other words, if you’ve never used expanding foam before, get the low expansion variety. Otherwise, you’ll have the daunting task of cleaning big messy globs of uncured foam off your walls, floors and skin. (Tip: Adding more expansion foam is easy, but removing it is difficult.)

It’s important to note here the terms “low expansion foam” and “high expansion foam” should not be confused with the terms “low density” or “high density” foam. Density refers to the number of pounds per cubic foot a foam weighs once it’s cured. For example, when an expansion foam product is said to have the density of “two pounds,” that means the foam has a density of “two pounds per cubic feet.” Furthermore, low and high expansion foam can have low, medium or high density.

Expansion Foam & Curing Agents

How much expansion foam expands also depends on its curing agent -- meaning, does it come as a one-component, no curing agent formula; or two-component, “A” and “B” (curing agent) formula?

  • One-Part polyurethane and latex expansion foams (“can foams”), do not come with accelerant curing agents. Instead, the foam cures (as a single component) by reacting with humidity. As such, it takes about 45-60 minutes to complete its curing and expands only about 2-3 times its original dispensed size. This mild expansion actually makes the one-component expansion foam suitable for eliminating small cracks, seams and gaps, which may be too big for caulk but too small for two-component expansion foam.
  • Two-Part polyurethane expansion foams aka two-component foams, in contrast, come as two separate components (agent “A” and curing agent “B”). As the agents are dispensed into the nozzle at application, agent “B” (curing agent) mixes with agent “A” to accelerate the curing time of the components down to 60-90 seconds. It is this fast chemical reaction that produces the higher expansion of two-component foam and what makes it suitable for filling large holes, nooks and crannies in walls, ceilings and floors.

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