I was always told that polyester thread is much stronger than cotton, & if you use it on a cotton quilt, it will eventually tear the fabric. I am certainly no expert here. I've always used cotton thread because I was told it was better; but I think you could use either one.
As far as mercerized, there's a good definition on wikipedia about what it means. Basically, the thread is soaked in chemicals to make the fiber swell which makes it easier to dye & softer. The process was discovered by John Mercer in 1844 & has been improved since then.

lets see if my sig works ;)

nope didnt work :(

lets see now

I use plain old Coat's and Clark for most of my sewing/quilting. Never had a problem. Works for me! :D

Many of the professional quilters are using polyester to piece as well as to quilt :wink:
I think the old polyester thread caused a lot of problems, but the new ones are just fine now :D:D:D

I use cotton to piece, and try to use all cotton when quilting baby quilts, I would hate for a piece of non cotton thread to wrapped around a little finger or toe.

JMHO

Thank you for the address

I use Aurifil cotton and cotton Masterpiece by Alex Anderson and polyester So Fine by John Flynn mostly. So Fine is so wonderfully great for piecing. I understand that Linda McCuen (sp?) used So Fine for quilting the $100,000 winning quilt "Bella" she did several years ago. Even professional quilters don't agree on what type to use, so experiment and see what YOU like. Just DON'T use those 10/$1 threads you find in discount stores. They are too inconsistent in the thickness and produce so much lint that they are TERRIBLE for your machine's tension discs. I can't tell you how many times a machine has come in for repairs in the shop I worked in, just to have it be the cheap thread that was causing the problem.

The theory is that polyester is stronger than cotton and eventually cut your fabric right on the seam. I have seen this happen.