Haha, this was the bag that I made from mostly fabric that was given to me for free. The $3.50 I paid for the Tula Pink remnant was the only thing I actually purchased for this. I had no fusible interfacing of any sort that I felt was stiff enough for this, so I used some stiff mystery fabric that was given to me as my main interfacing for the body and handle (seriously, I have like 3 yards of that fabric and I have no clue what's it's made of and it's too stiff/ugly for clothes). I also had some Thermolam insulation stuff left over from a coat I made, and since it's pretty fleece like, I used it to interface the bottom. As I was too lazy to baste in my interfacing, I used a glue stick to glue the interfacing to the fabric, which worked hilariously well. Yes, I used it on the knit and didn't have any issues.