There are alternatives and ways to maybe accomplish this though. If the amount of foam needed to be used pushes the limits try to combine it with the other foams and use them in thin blocks or spots. Since you are pouring aluminum as opposed to faster chill metals like bronzes etc. This can work for you if you make use of it, or be just a confusing quality if unawares. BTU HEAT absorption and TIME are consistent but as the aluminum soaks up the heat it seems to stay more nearly hard and then get to be like a softer putty.
Minutes pass but all of a sudden checking shows it's liquid.
Do NOT overheat now as the melting curve has just taken a squared jump up the scale of viscosity. And as the metal sits in the mold it again cools for a longer time than seems normal before it suddenly starts to get putty like and then harden more quickly. It cools to a harder stage again in a reversed and squared chart line. SO here's the rub. LIKE Create soaking gases and surface wise make one feel real grumpy later when you open the mold.