Pattern making is the heart of foundry practice.
Traditionally made of wood, patterns can be made of anything strong enough to withstand the pressures of being rammed in the sand.
There are a few considerations in making good patterns.
As the name implies, these patterns are made of foam. This can be bead board, like packing material, or expanded styrene insulation from a building supply store. (The pink or blue stuff.)
Usually cut with a hot wire cutter, the foam can be glued together to make larger pieces. Spray adhesive, white glue or low temperature hot melt glue guns have been used successfully. You might want to test an unknown glue to make sure it doesn't eat the foam you are working with before actual pattern making.