What is the difference between a blending brush and a shader brush?

A shader brush has a flat, densely packed head designed to pick up and deposit color with full intensity perfect for packing eyeshadow onto the lid. A blending brush has a fluffy, tapered head designed to diffuse edges and blend colors seamlessly in the crease and transition areas. Both are essential for a polished eye look, but if you can only buy one, the blending brush is more versatile.