You would need a small bit of glue just enough to coat the beads when mixed in a bucket. Use a stick to ensure th beads are spread out equally, as each bach is put in, hopefully illiminating any cold spots! When its dry it forms like a polystyrene slab.
If yournot use to expanding foam, it can make a right mess as it expand about 5x its size. The other thing is you would need to ensure the foam is open cell, as closed cell can cause issues.