What are some good brushes to apply a thick foundation with? like the Kat Von D foundation.
For thicker foundations you want to use a brush that has really dense and short tightly packed brush hairs. This will blend out thicker foundations and cream products a lot easier.
Try brushes like
Real Techniques Expert Face Brush $9 at Ulta, Walgreens, Walmart and Target
Sigma F80 Flat Kabuki Brush $24 online here
Marc Jacobs The Face 2 Sculpting Foundation Brush $48 at Sephora