Mixing Batting
 

I have a quilt I want to "enlarge" from a queen to a king size. I plan to add one or two rows of blocks on just one side. I don't know which batting I originally used but I'm 90 percent sure it was wool. Will it matter if I use an 80/20 poly cotton like Warm & Natural for the added blocks? Or do I have to stick with wool?

Oh, dear. I am no expert, but it just doesn't seem like a good idea to mix types of batting which, as I understand, has different shrinkage rates, etc. based on type. Since you are only adding a couple of rows, why not use the wool that you feel 90% certain was originally used? That seems best, at least to me.

My guess would be that the battings would work best if they were at least similar. My experience with wool batting is that it gives more definition to the quilting than cotton or cotton/poly. Plus, it has a higher loft than the others, while being softer. If you were adding blocks all the way around the quilt, even if it looked a little different than the center, it wouldn't look bad, but one or two rows on one side might not being pleasing. I do like to piece together my batting scraps and sometimes I have a little trouble telling one type from another, but I figure if they are that similar, it will work ok. So far so good. But, wool is a different story. I would go for the wool if you feel 90% sure.

battings will shrink at different rates when washed. I would buy a larger batt and save the smaller piece for a smaller quilt. JMHO

you should be able to tell by looking if it is wool batting vs warm and natural. And i would not mix those 2 up because wool batt is going to give a loft look to the quilting and cotton will be flat.

I think you're all correct, and I should stick with wool batting for the additional blocks. Thanks for your help.