When out of the drier..............iron and use spray magic sizing.

I have used fusible fleece in some table runners, but 95% of the time I use Warm & Natural batting, it seems to work the best for me.

FELT, FELT, FELT! Comes 60" wide from JoAnns (wtih a coupon) all poly - does not shrink and washes well. Table runners and small wall hangings lay flat and bindings don't ripple at all. That's all I ever use and have several customers that now use it too. I buy the neautral color most and have used black on occasion. Try it at least once.

I would think problems would creep up if it were not quilted enough. If quilted enough I think it would be unable to shrink or shift.

I use a low-loft polyester

I made 3 table runners, I prewashed fabrics and quilters flannel, which I used as the batting. It worked great and so far, no problem, they lay flat and look pretty good.

For wall hangings, table runners or placemats i only use flannel for batting. I wouldn't recommend poly batting at all....wall hangings won't hang straight if poly bat is used

I use Hobbs Premium Poly-Down. It lies flat and washes well. I don't prewash my fabrics and they turn out beautifully.

It's your cottons that are shrinking and making your work look messy, polyester is plastic, it won't shrink. But if it gets hot enough, will melt. That's why you can't use a hot iron on any garments made of the material. They all say, use a cool iron (you might as well use none! LOL) Whenever I wash a table runner, wall hanging or place mats, etc., they are hung to dry. People ruin more beautiful things using dryers. What's the fixation with dryers?

Another solution is to make your own jelly roll from 2-1/2" strips of prewashed fabric.

It sounds to me like it bothers you more than it does your cousin. She's probably just happy that you thought enough of her to make her something special.