Best Seed Bomb material??

I am gonna do a seed seed bomb making demo & hands-on at Eagle Days at Squaw Creek on Dec. 3 & 4.

I am looking for recipes to make the constituent material. Needs to be cheap but effective. Will be making seed bombs of native wild flowers and milkweed.

Anyone with experience? TIA

I have been meaning to try making some, but have not yet.
I was going to try the cheap clay from dollar stores.
I do not know whether that will work.

I've not tried, but if you google "seed bomb recipes" you'll get a lot of hits.

Karen