i know that fine sheets today have a thread count of 300-400. that means that if you have a STRONG magnifying glass and counted the threads, lengthwise and crosswise in a single inch, that's the total number. good sheets start at 200. below that is okay sheets. the thing that makes the real difference is the quality of the cotton. the longer the staple, the finer the quality.
so, think spaghetti.. you have very fine spaghetti, you stand it up in a glass. if you count the strands you have 400 pieces. now do the same thing with thick spaghetti. now count. you only have 200 pieces. same item, same glass. but because the spaghetti was thinner, you can get more of them=higher thread count. vs thicker, less strand=lower thread count.
add to that the quality of the thread. it can be indian cotton, which is coarse and rough because that's what is able to grow in that climate and is very short. it can be american cotton, which is okay, because it's long enough to not have too many stops and starts. and you have egyptian cotton, among the finest in the world. when they spin cotton, they overlap the strands onto each other to get the length they need for weaving. if they start with poor quality, they have to weave in more overlaps. that makes it rougher and it wears out faster. so the longer the strands they begin with, the fewer overlaps they have and the smoother the 'hand' is.
the finer the threads are, the smoother the fabric ends up being, the tighter the fabric can be because the ultra-thin threads can fit more into one square inch of finished woven product. whew!
around 15 years ago there started to be this public craving for fine, expensive sheets, when actually hardly anyone complained about them before. everyone thought they were entitled to have what only the wealthiest had enjoyed before. but when a pattern is printed on sheets, like white print on white sheet, that print stuff is hard and stiff and doesn't breathe like cotton. goodbye, quality!
so for quilting, the thinner thread sheets are not the best. they have the thinnest threads. very nice and smooth to sleep on, but they wear out quickly because....they are thinner.
and that is the story of thread count.