Polar fleece is a modern synthetic first developed at Malden Mills in Lawrence Massachusetts in the late seventies. It is really a man made wool. Unlike wool though it is very light and in hydrophobic, that is it doesn't absorb moisture. It washes well and dries quickly. It can be made partially from recycled plastic bottles and can itself be recycled into Polar fleece garments after use.
I wear polar fleece (now marketed under the name (Polartec) every day in the fall and winter, head to toe. When I paint outside in the winter it is the mainstay of my insulation. Polartec is a wonder product. There is an interesting story that goes along with it too.
The third generation owner of Malden Mills Aaron Feurstein developed the fabric and decided not to patent it so that others could make it too. This was an early sign of the kind of guy Mr Feurstein was.
On December 11, 1995, the mill burned down. Aaron then did an heroic thing, cashing the fire insurance check, he used the money not just to rebuild, but to keep all 3,000 workers on the payroll for the six months it took to reopen the factory. That cost him millions. He said that his lifelong study of the Talmud made him believe it was the right thing to do.
Ultimately the action cost him the company in bankruptcy court. The company was bought by another entity though who relieved him of his position as CEO. But the company and its workers still exist making not only Polartec used in many different manufacturers like LL Bean and Northface but producing weird high tech fabrics for the military. He was given the Peace Abbey Courage of Conscience Award on March 13, 1998 for his commitment to his workers and Lawrence, Massachusetts. Lawrence is a pretty hard bitten town, throwing 3000 workers out of their jobs would have been a catastrophe for Lawrence. It didn't happen because Aaron made sure it didn't happen, and was willing to suffer the consequences. A company formed of former employees still markets the material from Lawrence and their web site is here.