I know fabric shrinks irregularly - more widthwise than lengthwise; but what about batting? Does 100% cotton batting shrink evenly, or unevenly? What about Hobbs wool, or silk batting? What about silk batting, should it be washed at all. I have finally bought into prewashing and shrinking my fabric to avoid irregular shrinkage, but really don't know about the batting.

I would also like to know about the wool batting...according to the packaging, it can be washed in cool water, but needs to dry flat....not sure about how that is going to work in the winter....

batting shrinks a little bit...depends on the batt and it will tell you how much on the packaging. it also depends on the amount of quilting. a heavily quilted quilt will not shrink as much as a loosely quilted one. there are plenty of batts out there that do not shrink..
some times you can get swatches (6" squares) of different battings...you could test to see ... i've been making quilts for quite a long time now and have never worried about a batt shrinking. I love wool batts they are the best! i do not pre-shrink batting, if i want a batt to not shrink i buy one that doesn't.

There are places online where you can find out how much a specific batting shrinks. Sometimes this is printed on the packaging. A lot of cotton batting shrinks a maximum of 3%; however, a specific cotton batting could shrink considerably more or considerably less than this. There are many different ways even just cotton battings are manufactured, it's really impossible to give a standard for cotton.

Hobbs wool batting shrinkage is posted online -- somewhere between 1% and 3%, if memory serves me correctly. It can be machine washed and machine dried without excessive shrinkage.

Much depends not only on fiber content of the batting, but also on how the batting was manufactured (traditional, needlepunched, needlepunched through scrim) and also on the specific manufacturer.

One batting that does not shrink or change shape at all is 100% polyester batting, I think.

Oh, yes, and the amount of quilting affects amount of shrinkage also. Harriet Hargrave showed us a quilt she had made out of un-prewashed flannel (which has a reputation of shrinking badly). It was closely quilted by machine, and she measured it before and after it was machine washed and machine dried; very little shrinkage.

that is a really good question i will be watching answers