Geraldine, I've always used thin batting like Warm n Natural. I suppose your choice would depend partly on if you plan to set hot things on it.

Donna

I have used Thermore batting for table runners. Low loft, but it gives the quilting definition. Lois

I use Warm and Natural for my table runners because that is what I use for almost everything. I buy it by the large roll so I always have it on hand.
Linda OH

I like to use flannel or even a medium weight interfacing. I prefer to have the runner be as flat as possible because containers for flowers, pottery/china, and other centerpieces sit more securely on a very flat surface.

Teresa

Teresa, that's my concern....I'm afraid that things will topple over. I won't be doing a lot of quilting on the runners but I do want them to remain flat.

Thanks for the replies. They are appreciated.
I'm still not sure what I will use.

~Geraldine