Polar fleece

Polar fleece is a soft insulating fabric made from a type of polyester called polyethylene terephthalate (PET) or other synthetic fibers. Other names for this fabric are "Polar Wool," "Vega Wool," or "Velo Wools." Despite names suggesting the product is made of natural material, polar fleece is 100% polyethylene terephthalate.

Polar fleece is used in jackets, hats, sweaters, sweatpants, cloth nappies, gym clothes, hoodies, inexpensive throw blankets, and high-performance outdoor clothing. It can be made partially from recycled plastic bottles and is very light, soft and easy to wash.

One of the first forms was Polar Fleece, created in Massachusetts in 1979 by Malden Mills, now Polartec LLC. This was a new, light, and strong pile fabric meant to mimic—and in some ways surpass—wool. Aaron Feuerstein intentionally declined to patent Polar fleece, allowing the material to be produced cheaply and widely by many vendors, leading to the material's quick and wide acceptance.

A lightweight, warm, and soft fabric, fleece has some of wool's good qualities but weighs a fraction of the lightest available woolens. Polar fleece garments traditionally come in different thicknesses: micro, 100, 200, and 300, with 300 being the thickest and least flexible.

It is hydrophobic, holding less than 1% of its weight in water. It retains much of its insulating powers even when wet. It is machine washable and dries quickly. It is a good alternative to wool (of particular importance to those who are allergic or sensitive to wool). It can also be made out of recycled PET bottles, or even recycled fleece. Despite its fuzzy appearance and feel, it is not flammable, but instead melts when exposed to flame.

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Wikipedia