Almost any organic liquid in which your other chemicals are soluble, and which have a low boiling point can be used. You will see in my RG profile that we have frequently used diethyl ether as a blowing agent, but also diethyl ether / pentane blends, and of course pentane itself. All work very well, but there are interesting differences in terms of pore size for one given resultant density.

Alain

Why do you want to use physical blowing agents, and especially such increasing fire problems in fridge foams? The standard since the late 80ies is to use polyurethanes with carbon dioxide as the blowing agent (from isocyanate water reaction). You need special stabilizers to get a high closed cell content such as TEGOSTAB B8143. If you want to use physical blowing agents FEA 1100 is recommended.