What kind of foam should I get for drum cases?

I am buying some cases for my drums soon, and do not want to spend the extra money for the ones with foam in them. The cases I am buying are the Humes and Berg Enduro series. What kind of foam should I get to cut out and put inside them, and where can I buy it?

There is a sort of foam, which i can’t name you because i do not know it’s technical term. But it is made in Europe and the colour is in dark grey. I bought mine from brooklyn. But i’ve seen them on ebay before.