If you go to the website for your brand of batting, they will probably have info on prewashing. The Warm and HObbs companies do, you will have to check for other brands. Depending on the project I sometimes preshrink cotton batts.

I recently washed my Warm and Natural batting, because I was curious as to the amount of shrinkage. The batting was 80x80" before the wash; it shrank less than 1/4" in each direction! That convinced me that pre-washing is not necessary (I do prewash all fabrics).

I do not prewash batting (or fabric). I don't see the need and it just delays the time before I can start quilting.

I do not normally prewash batting, but may in the future. My last bolt of W&N had amusty smell. I put cut pieces in dryer with a vinegar soaked small towel. Smell gone and wrinkles from roll gone.

I prewash my batting in warm water and stick it in the dryer. I use the 80/20 and throw in warm dryer. Have had no problems. I just can't tolerate the smell from being in the plastic wrap bag. I have thrown polyester in a low heat dryer and check after 10 minutes. No problems.

Read the instructions that come with the battingt!!!!!!!!!!

I have turned a couple of what I thought were washable battings into mush. ( there were no instructions - I just went ahead and washed)

I bought a Quilter's Dream batting - on the BACK of the label - in small print - it said "do not wash before quilting"

I inquired of both Quilter's Dream and Hobbs, and their reply was, we do not recommend pre-soaking the batting. But on the Hobbs package, they recommend experimenting to see what effect you prefer (pre-soaked or unsoaked). So I wonder if they just have the pat answer (do not pre-wash) because they think people will not take the care to do it properly.