1. It is a bit different to work with, as you have to dab a brush into it without lifting the hair if you are using continuous strand mat. I use it with epoxy to make decorative corners that won't be filleted for paint
. Sort of a sheet rock tape grade inside corner.
2. Most Mat that is available for sale
today, is soluble in epoxy.
It used to be that it was soluble only in styrene, if you got some off an old roll from the early 2000's, its a possibility that you got the stuff that lays out like cardboard in epoxy.
3. You don't have to use Mat with epoxy. Most Biax is 1708, which has a mat backer that makes it compatible with polyester and vinylester, without having to add a layer of mat between layers of biax. It has 8 ounces per square yard of mat attached to the back, the 08 designates that.
If you buy 1700 biax, it has no mat backer, and with epoxy you don't need any mat in between layers. You wet out with less resin as it takes 17 ounces of resin to wet out a yard, compared to 25 ounces for a yard of 1708.
I like 1708 for big overhead work in epoxy, unless the 1700 stuff is stitched very tightly the 1708 is much less "stringy" where the stitching doesn't come out and wind
around your air roller quite as bad. This is more so if you have to cut a piece of cloth across the bias.