I have been making purses lately, and am confused between interfacing and stabilizer. Are they interchangeable if the weight is approx the same? I use quite a bit of fusible fleece, since that is what is suggests in the Bow Tuck pattern, but some I want to make (and have made) call for fusible interfacing, some fusible and some sew-in (does it matter?)and is Craft Fuse by Pellon the same as fusible interfacing? I have one pattern that calls for very stiff iron-on interfacing in German #250 (what ever that is), so I used a stiff one I already had and it was so stiff, I couldn't sew thru the layers! I bought med. weight stabilizer (Pellon #40)-It isn't fusable-can that be used for med. weight interfacing? Hope this makes sense-could really use some clarity!