Cheap Joe's Golden Fleece brushes are made from 100% Toray Nylon. Toray nylon is arguably the best synthetic brush hair out there. It's used by many companies in a variety or colors and hair shapes.
The really great thing about synthetics is each hair can be optimally molded for a brush. Toray is a Japanese company that patented the type of nylon. It's also used for fishing line! But don't try to make a brush from fishing line. The hairs really are tagged (or frayed) to microscopically pick up water droplets. Synthetic brush hairs are some pretty great technology that makes watercolor affordable to everyone, not just people who can afford kolinskys!
The Golden Fleece brush handle is laquered hardwood. The website states the brush hairs are made from varying sizes of nylon for optimal shape. It feels nice, but a little heavy in my hand.