Green Foam Shrinkage

I'm wondering how, "use of Poly/Iso Foam Core." can produce a "green" product, but never mind.

This is true of everything in the universe. When you heat it up it expands. Cool it off, it contracts.

So, you mix the foam and get a reaction that produces a gas. It is exothermic, so it produces heat too. During this time the foam hardens trapping the gas and producing a low density material. Just for grins, lets say that the foam's reaction heats it to 120°F. It then "freezes" (or hardens) at that temperature. If room temperature is 78°F, you've got a 42°ΔT. It will shrink.

The trick is to keep the cure temperature as close to the service temperature as practical.

Since you are developing this product , you will be able to verify if the product shrinks just from the thermal expansion that lynlynch described elsewhere. I believe that verification should be very straight forward. Measure the volumes of a known quantity of various samples of your insulation long at different temperatures. You will of course have to wait a sufficient amount of time to be sure that the entire volume of insulation has reached a thermal equilibrium. I would make sure that I used old foam core insulation because I suspect that the thermal expansion is not the dominant effect you have here.

I suspect that the dominant effect is that the foaming gas produced pressurizes the little bubbles made in this process. Clearly this does happen because unrestrained this liquid fills the space of a cavity. Overtime the internal gas pressure slowly drops thus shrinking the foam. This is why I recommended doing the thermal expansion measurements with old foam. If this is the dominant source of shrinkage it would be useful to measure this shrinkage, too.

Now why bother to identify and measure the two methods of shrinkage. The thermal expansion will always happen and cannot be stopped. Likely this expansion though will not be all that large. The gas pressure shrinkage will happen only once.

There are only two methods I know of to reduce the effect of the gas pressure shrinkage. The first I already implied, wait long enough for this shrinkage to happen before installing the insulation. The second is to have enough cohesion with the containing surfaces so that shrinkage happens at another location. The trouble with the latter solution is that this relies on the structural integrity of the variable surface.