I think there's a big difference between the 2. It seems to me the Bosal is more like a batting & the Peltex is definitely a heavy duty interfacing. I have made bags with Peltex and they are really sturdy. I have Viking Designer I and SE machines which sewed thru 2 layers of peltex, plus fabric & lining. I had to wrestle with it a bit, but they sewed OK.
BTW, if you decide you really like the Peltex, you can get a similar product at a much better price at longcreek mills:
http://www.longcreekmills.com/product/stabilizer3.html