Fleece

What it is

Polar fleece is an insulating, napped polyester fabric — its surface is raised into a soft pile. It can be made from recycled PET bottles or recycled fleece ^[1].

A note on names: in hoodies and sweatshirts, “fleece” often means something different — a cotton or cotton-blend knit with a brushed inner side. This page is about polar fleece.

Why it’s warm

The raised pile traps air, and trapped air is what insulates. Fleece is sold by weight — micro, 100, 200 and 300 grams per square metre — and heavier, higher-loft grades are warmer ^[1].

How it behaves in the wet

Polyester is hydrophobic. When wet, fleece holds less than 1% of its weight in water and dries in about one to four hours ^[1]. But it is not waterproof or windproof, and it loses most of its insulation once it’s wet ^[1] — so in rain it needs a shell over it.

The trade-offs

• Static and pilling. Fleece builds static that picks up lint, dust and pet hair, and lower-quality fleece pills ^[1].
• Microfibres. Washing synthetic fleece releases tiny plastic fibres. One study measured up to about 2 grams per garment per wash, with top-loading machines releasing about seven times more than front-loaders, and mechanically aged garments shedding more than new ones ^[2].

A bit of history

An early version, Synchilla, was developed by Malden Mills with Patagonia in Massachusetts in 1979. Malden Mills chose not to patent it, which helped it spread quickly ^[1].