Fleece is made from superfine polyester yarn. It is a synthetic fabric that can be produced using a number of different techniques and materials. Modern polyester is typically made from recycled products, especially soda bottles. Once the fibers are brushed, the polyester material increases in volume to give the fleece its unique feel.
When first invented in 1979, fleece was designed to mimic the feel of wool. The polyester yarn was wound tightly into multiple layers to recreate the thickness of wool. Because of the synthetic materials, fleece became very dense, but it also became light-weight like a terry cloth.
Three different thicknesses are commonly produced using these methods: 100, 200 and 300. The higher the number, the thicker the fleece is and the more layers it has. Even though fleece can be made thick, it is still not windproof and does not absorb moisture.
While fleece is mostly made from recycled products, the continued manufacturing of fleece relies on fossil fuels. Raw materials still need to be used in order to create some versions of fleece. The greenhouse gases produced during manufacturing are about the same as wool, but fleece tends to be more durable because it is using recycled materials.