Polar fleece, usually referred to simply as "fleece," is a soft napped insulating

Thermal insulation

Thermal insulation is the reduction of the effects of the various processes of heat transfer between objects in thermal contact or in range of radiative influence. Heat transfer is the transfer of thermal energy between objects of differing temperature...

 synthetic fabric

Textile

A textile or cloth is a flexible woven material consisting of a network of natural or artificial fibres often referred to as thread or yarn. Yarn is produced by spinning raw fibres of wool, flax, cotton, or other material to produce long strands...

 made from Polyethylene terephthalate

Polyethylene terephthalate

Polyethylene terephthalate , commonly abbreviated PET, PETE, or the obsolete PETP or PET-P, is a thermoplastic polymer resin of the polyester family and is used in synthetic fibers; beverage, food and other liquid containers; thermoforming applications; and engineering resins often in combination...

 (PET) or other synthetic fibers. One of the first forms was Polar Fleece created in 1979 by Malden Mills, now Polartec LLC., a new, light and strong pile fabric meant to mimic and in some ways surpass wool. Fleece has some of wool's finest qualities but weighs a fraction of the lightest available woolens.
Polar fleece is used in casual jacket

Jacket

A jacket is a hip- or waist-length garment for the upper body. A jacket typically has sleeves, and fastens in the front. A jacket is generally lighter, tighter-fitting, and less insulating than a coat, which is outerwear...

s, hats, sweater

Sweater

A sweater, jumper, pullover, sweatshirt, jersey or guernsey is a garment intended to cover the torso and arms. It is often worn over a shirt, blouse, T-shirt, or other top, but may also be worn alone as a top...

s, jogging bottoms/sweatpants

Sweatpants

Sweatpants are a casual variety of soft trousers intended for comfort or athletic purposes.In Britain, Australia and New Zealand they are known as "jogging bottoms" or "track pants".- Design :...

, gym clothes, hoodie

Hoodie

A hoodie is a sweatshirt with a hood. The characteristic design includes large frontal pockets, a hood, and a drawstring to adjust the hood opening. They are sometimes worn with sweatpants. Some hoodies have zippers on them to allow easy removal much like a jacket...

s, inexpensive throw blankets, and high-performance outdoor clothing, and can be a vegan alternative to wool

Wool

Wool is the textile fiber obtained from sheep and certain other animals, including cashmere from goats, mohair from goats, qiviut from muskoxen, vicuña, alpaca, camel from animals in the camel family, and angora from rabbits....

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