Fleece Weights Explained: What 100, 200 and 300 Actually Mean

Fleece is the most-owned and least-understood midlayer in the wardrobe. The numbers on the label — 100, 200, 300 — mean something precise, the fabric has one defining weakness that explains almost every "my fleece isn't warm" complaint, and the price range from supermarket to specialist spans a factor of ten for reasons that only sometimes matter. Here's what's actually going on inside the fuzz.

The numbers are grams per square metre

The 100/200/300 system comes from Polartec (originally Malden Mills), whose Polartec Classic fabrics are specified at roughly 100, 200 and 300 g/m². The industry copied the convention, so today "a 200-weight fleece" is shorthand understood across brands even when nobody involved uses Polartec fabric.

Weight tracks warmth almost linearly, because what you're buying is thickness — more pile, more trapped air:

Two caveats. First, g/m² is fabric weight, not garment warmth — a dense, short-pile 200 and an airy, lofty 200 insulate differently, and loft is what matters. Second, most non-Polartec "fleece" is unlabelled; if the garment feels like a sweatshirt it's around 100-weight, like a proper fleece jacket it's 200, and if it could stand up on its own it's 300.

How fleece insulates — and the wind problem

Fleece is polyester knit with the surface brushed into a raised pile. The pile traps a layer of still air, and still air is the actual insulator — the polyester is just scaffolding. This is the same mechanism as every insulation, from down to wool: hold air still near the body.

The catch is the word still. Fleece is extremely air-permeable — that's deliberate, it's what lets sweat vapour escape so well — but it means any wind above a gentle breeze blows straight through the pile and strips the warm air out. A 300-weight fleece on a windy ridge can feel colder than a 100-weight under a thin windproof layer. This isn't a defect; it's the design trade-off. Fleece is a midlayer: it assumes something windproof goes over it. Worn as an outer layer, it only works in calm conditions, and the "windproof fleece" variants with a laminated membrane fix the wind problem by sacrificing most of the breathability that made fleece worth wearing.

The flip side of air permeability is fleece's genuine superpower: it is hydrophobic and holds almost no water. Polyester absorbs under 1 % of its weight in moisture, so a sweated-through or rained-on fleece dries in an hour of body heat and keeps insulating meanwhile. This is why fleece remains the default midlayer for wet climates and sweaty activities, decades after fancier fabrics arrived.

Grid fleece vs. classic fleece

Classic fleece is a uniform pile. Grid fleece — Polartec Power Grid, made famous by the Patagonia R1 — knits the pile into a waffle of raised squares with channels between them. The squares trap air against the skin; the channels move moisture and let excess heat vent. The result is a fabric that insulates like a heavier fleece while weighing less, packing smaller, and dumping sweat dramatically faster.

For anything aerobic — ski touring, winter running, fast hiking — grid fleece is simply better, which is why the R1 pattern has been copied by nearly every technical brand. For standing around, classic fleece's uniform pile is slightly warmer per euro and feels cosier. Polartec Alpha sits further along the same axis: a lofted insulation originally developed for US special forces, so air-permeable it behaves like "active insulation" — warm while moving, ventilating constantly. It belongs in the same conversation as the synthetic fills covered in the down vs. synthetic guide, rather than as a fleece replacement for everyday use.

Fleece vs. wool, fleece vs. puffy

Against a wool midlayer: wool is warmer when damp in absolute terms and doesn't smell, but it's heavier, slower to dry, and pricier per degree of warmth. Fleece wins on weight, drying speed and cost; wool wins on odour and that it keeps buffering moisture rather than just passing it through. (For the base-layer version of this fight, see merino vs. synthetic — the trade-offs rhyme.)

Against down or synthetic puffies: a puffy gives far more warmth per gram and compresses to nothing, but it's fragile, expensive, and clammy during exercise because its shell fabrics block airflow. The practical split:

• Moving → fleece (or grid fleece). It breathes, survives abrasion from pack straps and branches, and shrugs off sweat.
• Static → puffy. Warmth per gram wins when you're not producing heat.
• Cold and moving hard → fleece while moving, puffy thrown over everything at stops. This is the standard system, and where it fits in the bigger picture is covered in the layering system guide.

Pilling and care

Pilling — the little bobbles — happens when loose fibre ends tangle under abrasion. It's cosmetic at first but a pilled, matted fleece has measurably less loft, so it's also a slow warmth leak. Cheap fleece pills fast because it's knitted from short staple fibres, loosely; good fleece uses longer fibres in a denser knit and often an anti-pill finish.

Care is easy and mostly about restraint: wash cold, inside-out, on a gentle cycle; no fabric softener (it coats the fibres and kills wicking, same as with socks); air dry or tumble low. Keep fleece away from velcro, which rips pile out on contact. One honest downside worth knowing: every wash sheds polyester microfibres — a filter bag such as a Guppyfriend reduces it, and washing less often (fleece rarely smells after a day's wear) helps more.

€15 supermarket fleece vs. €100 technical fleece

They are the same material — polyester pile — and the cheap one genuinely insulates. The money buys:

• Fibre and knit quality. Anti-pill, denser knit, loft that survives fifty washes instead of five.
• Cut. Articulated sleeves that don't ride up when you reach, a hem that stays under a harness or hipbelt, a collar that actually seals.
• Grid or stretch constructions that a €15 fleece never has.
• Details. Flat seams under pack straps, zips that don't snag, thumb loops, chest pockets that sit above a hipbelt.

When is the cheap one fine? Often. Walking the dog, the commute, around the house, as a disposable layer for muddy jobs — a €15 fleece under a windproof jacket is 90 % of the warmth of anything. Pay up when you'll wear it hard and often: daily winter use, aerobic sport, under a shell on multi-day trips where drying speed and a non-bunching cut stop being luxuries. A €40–60 fleece from a reputable outdoor brand is usually the sweet spot; above that you're paying for grid constructions and cut, which only athletes and frequent users will feel.

FAQ

Is a fleece enough as a winter jacket? In calm, dry cold down to around 5 °C at a brisk walk, a 200-weight can be. Add wind or standing still and it falls apart fast — fleece assumes a shell over it. If you're actually shopping for an outer layer, start with the parka buying guide instead.

Can I wear two fleeces instead of one thick one? Yes, and it works — two 100s trap air between the layers and roughly match a 200–300 with more flexibility. It's bulkier and the layers can bind at the arms, but as a use-what-you-own strategy it's entirely legitimate.

Why does my fleece spark and crackle? Static. Polyester holds charge in dry winter air, especially fresh from a tumble dryer. Air drying and a damp-hand wipe-down fix most of it; it's annoying, not a quality signal.

Does fleece lose warmth over time? Yes — the pile mats down and pills, losing loft. A dense, anti-pill fleece keeps most of its warmth for many years; a cheap one can halve its effective loft in a season of heavy use and washing. If the pile looks flat and shiny, the insulation is mostly gone even though the garment looks intact.

The one-line answer

The number is grams per square metre — 100 for moving, 200 as the default, 300 for standing still — and every fleece needs something windproof over it, because what you bought is trapped air, and wind takes it away.