Marvin ..NO ..dont use it ..its not what we are talking about when we mention foaming a mask. You want a two part soft polyfoam ( try silpak) to foam a mask outside of the mold will be tricky. the foam by nature wants to expand and push out ..with out the mold, you are in danger of distorting it. however ..with a quick hand, pour in a small batch then use a chip brush to quickly paint up the sides of the mask with foam before it starts to rise. thats all the time you have ..maybe 30 seconds top. after that, the polyfoam will start to rise ..if you touch it, it will collapse on itself and become a mess. let it sit, cure ..then repeat. I say let it cure because if you try another immediate pour, you run the risk of painting up on the first batch as its still "kicking" thereby collapsing that. What you are doing is creating a foam skin inside the mask for support. It will not be a snug to your face mask. to do that, you would want the mold and a dummy head/lifecast to insert into the mold ( with polyfoam release coating it) then you would foam around that ..the original mold will prevent distortion of the latex mask.
hope this made sense