Key takeaways
- Fleece is a soft synthetic (usually polyester) insulating fabric used mainly as a mid-layer.
- It stays warm when damp, dries fast, and breathes well — but blocks little wind on its own.
- Graded by weight: lightweight (100), midweight (200), and heavyweight (300).
- Pairs with a base layer beneath and a wind/rain shell over it for full weather protection.
How fleece works
Fleece is a napped synthetic fabric, usually polyester, whose raised fibers trap a layer of warm air against the body. Because the fibers themselves don’t absorb much water, fleece keeps insulating when damp, dries fast, and breathes well during activity — but the same open structure lets wind blow through, so it needs a shell over it in breezy conditions.
Fleece weights
- 100-weight — light and breathable; high-output activity and mild cold.
- 200-weight — the versatile all-round mid-layer.
- 300-weight — warmest; cold, low-activity conditions.
On a cold, breezy hike a hiker wears a base layer, a 200-weight fleece for warmth, and a windbreaker on top — shedding the shell on the climbs when the fleece’s breathability keeps them from overheating.
Where it fits in a layering system
Fleece is a classic mid-layer: base layer underneath to wick sweat, fleece for breathable warmth, and a wind or rain shell over the top when needed. Its warm-when-wet, fast-drying nature makes it more forgiving than down for active, variable days.
The bottom line
Fleece is the workhorse mid-layer of outdoor clothing: warm-when-damp, fast-drying, and breathable enough to wear on the move. Pick the weight to match your output and conditions, layer a base under it and a shell over it, and fleece handles the broad middle of three-season warmth reliably and affordably.
Frequently asked questions
What is fleece and why is it used outdoors?
Fleece is a soft, napped synthetic fabric that insulates by trapping warm air in its raised fibers. Outdoors it's prized as a mid-layer because it stays warm when damp, dries quickly, and breathes well during exertion — though it needs a shell over it to block wind.
What do the fleece weights (100, 200, 300) mean?
They refer to the fabric's weight in grams per square meter, a proxy for warmth and thickness. 100-weight is light and breathable for high activity, 200-weight is the versatile all-rounder, and 300-weight is the warmest for cold, low-output conditions.
Is fleece or down warmer?
For its weight, down is significantly warmer and more packable, but it fails when wet. Fleece is bulkier and less warm per gram, yet it keeps insulating when damp, breathes during activity, and dries fast — which is why fleece is a moving mid-layer and down a static warmth layer.
Sources
- Fleece & synthetic insulation — Polartec
- Layering systems — The Mountaineers