Half-zip reversible jacket made of Polartec 300 shearing fleece and water-resistant nylon. Polartec 300 is the thickest and most insulating type in the "Polartec Classic" series of fleece materials manufactured by Polartec. It is lightweight and excellent in heat retention, breathability, and durability. The fabric is more substantial than I expected, and I was looking for something thinner, so I'm letting it go.