Its open cell foam. The trimmer looked like a sawzall with a 3 foot long blade on it. I tried cutting the foam with a razor to do some final trimming around outlets and in corners and it didn't cut easy, but the guys electrical machine just sheared through the foam leaving a very clean, flat surface. The R value for open celled foam isn't as good as closed cell, ~1/2 the R for ~1/2 the price. Its comparable to fiberglass batts, but with much better air resistance.