My church group makes quilts for Lutheran World Relief and normally we tie with whatever yarn we have and it has worked. Now LWR is asking that we use crochet thread instead of yarn, so we will have to try that, maybe using it a couple threads thick would look alright.

I work with a group that ties a lot of quilts for charity type applications, and some of our members are in their upper 80's and older. They have trouble pulling through the worsted weight yarn, and I think it looks "frumpy", so I have them use crochet cotton. It comes in lots of nice colors. Embroidery floss can come in lower grade brands and break too easily, and is more expensive for our application. Crochet cotton we can get at thrift stores.

do you use a single thread or do you double it up?

I always use yarn and have for years.

yes, crochet cotton works best for me. I go to the thrift shop and find partially used balls of thread for about fifty cents. Never had a problem with them. Also if you find the variegated or metallic accented crochet cotton, it makes for wonderful accents in couching for crazy quilts. I also use some for raised pin-tucks.

I made a tie quilt for my daughter when she was very small and tied it with very narrow ribbon. The ribbon wants to come untied so I put a little dab of Fray Check on each tie and she still has the quilt today...she is 30 now... :P

I like to use #10 crochet thread that comes in a big ball. Much cheaper than embroidery thread. I also use Fray Check (the kind that stays soft) on each knot. I can't stand to waste my precious embroidery thread on ties. lol I have almost every color DMC makes - yes in numerical order in one two sided tackle box and two more compartment boxes. I feel the same way about my thread that most of you do about fabric.

I usually use crochet thread as it seems to outlast embroider floss and does not ball up as much as yarn - one ball of thread will do multiple quilts, too

I think they want crochet cotton,and was asked for because of the quilt washing & drying. Looks nice longer. I have used embroidery floss on quilts mostly for childern, because they can be tied tighter, they need to be washed more often, and they keep looking good.

Crochet cotton thread is what my husband's aunts and grandmothers used - my guild members either use it or six-strand embroidery floss. Variegated floss or multicolor floss can be very stunning. I've seen metallic floss used to tie small holiday wall hangings