Well, I am using the polytek f5. I think its a 5 density. I dont know if theres a shore hardness for the foams. The softest rubber ive found is 30.
This foams skinning properly in the mold but i have a theory why. Im working with alumilite locally to get a better foam working. They have a 3 thats nice. its like nerf but smaller, more uniform cell density. Its not ready yet.
Send me a pm about what your making and ill see if i can help you get what you want out of it.