Pellon fleece interfacing, sold with the interfacing in JoAnn's, 45" wide available in fusible or non fusible. I use the non fusible. Gives it body, but flat enough for a candle to be safe. Example:
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I too use the Pellon fleece non fusible. I like my table runners flat and this does it. Irish Rose -- I love your Spicy Spiral -- I put the pellon in the one I did too and it is great. The teacher I had when I started quilting again after about 15 years absence used this all the time.

I use flannel. Pre wash and it works great. Plus cheap to do!

I use thermolane....it is a very thin fleece type used in padded clothing........does not shrink when washed, so it must be a poly product...not in my sewing world now.....but I like that the best. I use JoAnn coupons when I need to buy more. gives enough loft for looks, but not thick and lumpy.......when quilted down...