Are you planning to wrap the foam, and so get the finished frame (positive), or do you want to make moulds out of foam (negative moulding). This determines wich kind of foam you want to use. For negative moulding, you would want to use epoxy tooling board, for positive foam wrapping, you might need low temp prepreg (ooa) and a foam like airex or rohacell.
It is not trivial to get a nice and straight frame with positive wrapping methods, as the vacuum bagging easily warps the flexible foam model during the cure process. A process called "Tube to tube" is easier to manage in terms of the quality of the final product, compared to get everything (or just the front triangle) in one go.

Hello,
I want to make a bicycle frame by prepreg vacuum bagging process . I am going to use foam as a mold.
I am looking for a foam to withstand the temperature that the prepreg needs to cure.
what type of foam do you suggest?