I use .25 and .125 diamond spray on felt and it works great but I may have to rethink my use felt after my conversation with Ed to the meet on Sunday. He told me that felt has some type of recoil or spring effect at the end of each pass which launches the dried diamond spray up in the air and and makes it easy to breath in. After 10-15 razors you could be breathing in considerable amounts of this stuff, this is why he uses light weight balsa. I never thought of that, I'm doing 3-4 sometimes 5 razors at a time so I see some balsa in my future,