I have used both light weight fusible interfacing didn't like the stiffness or weight of it. .
Next one starch. Liked it better I'd do a test run with the back of a t-shirt use both and see which works for you.

Really neat quilt! Thanks for all the info. My granddaughter also wants me to make her a quilt out of her favorite t-shirts and I found everyone's suggestions most helpful. I was afraid to tackle the job and didn't know how to even start. Like very much that several people posted pictures too.

You DO NOT have to use fusible interfacing. The too cool Tshirt website does not advocate that. I have made several T-shirt quilts and I generally do NOT use fusible interfacing. The only time I do use fusible interfacing is if the shirt was especially thin or it was a 'mesh' shirt with holes.

I have been reading some of the advice you have received. I have made two so far and have used a light weight fusible and been very happy with it. Without the stabilizer (fusible) my shirts were curling up on the edges. I did find out one thing that made the second one easier: put the stabilizer on BEFORE you cut the shirt to the exact size. Prep the shirt first by cutting off the sleeves and cut up the back and open it up. Cut off the excess fabric but do not cut to the exact size until the fusible is on. That really helped with the accuracy of the block; less stretching, etc. Good Luck.

I have made too many for clients. Beware, they become some what heavy (compared to a pieced quilt top) and be so careful that your favorite iron does not come into contact accidentally with the paint on one of the T-shirts.

I iron butcher paper squares on the back of the t shirt, then I sew the pieces to fabric sashes without removing the paper, I remove the paper before basting and quilting, I find the this way the quilt is softer and more pliable.

I haven't made one, however, my girlfriend has made several -the "trick" is to use fusible interfacing on the T-shirts, then square up to size you want as this stabilizes the knit in the T-shirts. She then uses sashing to complete the quilt.

The things I have read suggest French Fuse, which is really light weight with some small amount of stretch. I have not done an entire quilt yet, but have made a few tote bags and it worked great. My LQS machine quilts T-shirt quilts and they are great. I have seen ones that are all regular, same size blocks and ones that are more random. I love both. You can get the French Fuse with a coupon at JoAnns or Hancock....