Yes, you can use Dow Great Stuff spray foam on XPS foamboard!

I am posting this because I finally found an answer buried deep on Dow’s website after searching in vain for some time all over the internet.

I received conflicting information about this, with some people (in person and online) claiming that you can only use “approved adhesives” with XPS (this is true) and that spray foam would eat through the polystyrene (this, it turns out, is false).

Dow, makers of “Great Stuff” spray foam (-in-a-can) insulation actually recommend using the foam if you need to fill in a cracked piece of extruded polystyrene (XPS) foam board insulation.

Here is the evidence:

Depending on the size of the hole or crack [in XPS board] there are several possible materials that Dow recommends for use: For larger holes or cracks a spray in place polyurethane such as GREAT STUFF* or equivalent can be used.

So perhaps the keywords in this post will help someone else find this information: “Great Stuff” and other spray foam insulation in a can is safe for use with extruded polystyrene (XPS) foam boards.