What type of polyurethane foam board do I need to buy for blanks? I’m confused because it looks really sturdy in shaping videos and in real life polyurethane foam looks too soft and hard to sand? Do I need to use some type of body filler over it? Or do I need to buy a specific type of polyurethane foam board?
No filler, just fibreglass.
So how do I shape it before glassing? Regular Polyurethane foam is really soft… kind of sponge-like almost…
I think you might want to ask for ‘‘rigid’’ PU foam, the stuff that’s in couches isn’t used for surfboards 
And most PU sheet foam of the rigid variety isn’t done to the same criteria as surfboard-specific blanks, so it isn’t that useful either.
There’s these really obscure and hard to find things made out of polyurethane foam. They’re called “surfboard blanks”. (Weird, ain’t it?)
Good luck finding one, as they are also made with unobtainium.
Start at US Blanks, work your way around the world from there. Someone help me....Buford , Artic, Marco, Clark , Walker, WNC,,,,,,,,, Unobtainium,,,,,,,,ha ha........
Millenium is consistently putting out a high quality blank these days too.
I’d try to get some dimensions down on paper and use an already shaped board that you like as a reference. Take measurments off of the board so you can see what you came up with and what the board measures out at and then use that to make your final design. Keep it simple and have fun.
Co-sign on that.
Pretty consistent on the quality too.