I use yarn that I knit mittens with, works well and stays tied.

I use perle cotton. Washes very well and looks nice.

I'd like to use crochet cotton, and after I've tied the knot, slip it into the quilt so there are no tails. I'll be exhibiting the quilt, and although I would like the looks of no tails, I wonder what the judges would think.

We make a LOT of tied quilts for nursing homes, church shut-ins, etc. and we always use embroidery floss--all six strands, and double knotted.

I've used embroidery floss and sport weight baby yarn to tie quilts.

I like to use narrow satin ribbon, tie in a square knot and then in a small bow, for little girl's quilts. For older folks I've used a wider varigated ribbon that is marketed for crocheting and only tie in the square knot, leaving about 1-1/2" tails.

I'm making a quilt for a friend just diagnosed with breast cancer. She teaches music at a private Catholic school so sees every child for the 8 -9 years they are there. I don't work there and am not Catholic, but I know what a huge part of her life this is . sooooo I'm making a photo quilt with photo blocks of her family around a panel that looks like stained glass. I'm going to machine quilt around the panel and around each photo block - probably around each border too. THEN I'm going to put long ties that pull to the back of the quilt. I'm going to give it to the PE teacher - also a friend of mine - because she also sees every child. I'm going to have her get the children to tie knots and sign a notebook that they have done so. The staff of the school will also tie and sign. I'm hoping when I give it to her she can continue to have friends/family/visitors sign her book and tie a knot. (This would not fly in a public school - I teach in one - but I think will be a good thing for these children - and for my friend.)

So ... anything to add? Crochet thread sounds like my best bet. I'll tie the square knots to be sure they stay, but the visitors will keep adding knots. Should I leave them about ...3"? More? The backing has a stained glass look with pinks and greens so the thread will be those colors. I have never tied a quilt before ... or put photos on fabric ... so ... hoping for the best!