Thank you both. If you take a t-shirt or other knit you can "stretch" it. That means if you cut 100 squares and sew them together, they will get all "caty-whomp-ous" and out of shape. So the interfacing (spray adhesive, iron-in, or stickers causes the fabric to hold it's shape and not streach. The first batch of interfacing dh brought home for me wasn't strong enough for some of the knits and they would still manage to stretch, so I had to be very careful as I sewed.
I much perferred a thicker interfacing that held everything just right. Yes, Tigerbaby1981 you're exactly right. The next trouble with not using interfacing is that when you go to quilt it, the more dense your quilting is the more and more crazy stretch you see in your quilting.
I have a perinatal quilt from when I was first starting to work with knits and the center of the heart sort of swirls. It's a nice effect, but not what I was going for (the other reason they tell you to quilt from the CENTER out. :D )
I've added a photo of it, and if you look closely at the center you can see the "swirl".
The other thing I've noticed about working with these types of fabrics is that they are thicker than standard quilting cotton. Seriously, they are even thicker that fabric store cottong. This isn't really a problem it just takes a little getting used to (in my case I worked it the other way around and had to get used to how "thin" calico cotton is! :D )
See there in the center where the polka dots are? Yes, it's right there.
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