I love the Loew Cornell brushes for this technique. I bought a set of four from Michaels for use on fabric, but Michaels doesn't carry that brand now. The Art Minds brand Michael's sells is not quite as stiff as I like for this technique. I ordered individual brushes from Dharma Trading Company to add more sizes to my original set.
Order the Loew Cornell flat and round fabric painting brushes from Dharma.
http://www.dharmatrading.com/html/eng/3260-AA.shtml
The flat brushes 2, 4, 6, and 8 and the round brushes 10/0, 5/0, 0, and 2 are the ones that I prefer for the work I am doing.
Here is what Dharma says about Brushes For Fabric Painting:
Fabric painting brushes need to be stiffer, so you can press the paint into the fabric. Fabric paints have to be pressed down into the fabric as they are painted on. If you just lay a bead or layer on the surface, it will not grip the fibers and therefore will flake or chip off.
Silk Brushes vs. Fabric Brushes
Silk brushes are soft and soak up large amounts of dye. They are used for filling in areas and watercolor painting. Fabric brushes are stiffer than silk brushes, which helps to force paint or dye into the weave of fabric.
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