Thermal underwear fabrics compared
Warmth, softness, stretch and price all come from the fabric. Here are the seven fabric families we use for thermal underwear, with their typical weight, warmth and best use — the same table we walk buyers through before sampling.
| Fabric | Composition | Weight (gsm) | Warmth | Feel | Best for | Cost |
|---|---|---|---|---|---|---|
| Brushed polyester-spandex | 90–95% polyester, 5–10% spandex | 180–260 | ●●● | Soft brushed inside, stretchy, dries fast | Mass-market thermal sets, marketplace best-sellers | $ |
| Fleece-backed polyester | 90–95% polyester, 5–10% spandex, dense pile | 280–400 | ●●●●● | Thick, plush inside, smooth outside | Fleece-lined leggings, outdoor work, extreme cold | $$ |
| Acrylic-viscose “velvet” knit | Acrylic, viscose, spandex | 200–300 | ●●●● | Very soft, slightly fuzzy, warm to the touch | Women’s tops and turtlenecks; popular in Russia and Asia | $$ |
| Modal-spandex | 90–95% modal, 5–10% spandex | 160–220 | ●● | Smooth, silky, thin | Everyday layer under office clothes | $$ |
| Cotton rib and waffle | 95–100% cotton, or cotton-polyester | 180–260 | ●●–●●● | Breathable, classic feel; waffle traps air | Classic long johns, henleys, kids, sleepwear | $ |
| Polyester grid fleece | Polyester or polyester-spandex, grid-brushed back | 180–240 | ●●●● (active) | Wicks sweat, breathes, light for its warmth | Ski, hiking and winter sport base layers | $$ |
| Merino wool blend | 50–100% merino with polyester or nylon | 150–250 | ●●●● | Soft, regulates temperature, resists odour | Premium outdoor, multi-day wear | $$$$ |
Warmth is relative, for the typical weight shown. Cost is relative per piece: $ lowest, $$$$ highest. Exact compositions and weights are confirmed on your sample.
Choose by how the garment will be used
| Use | Recommended fabric | Weight |
|---|---|---|
| Sleeping and lounging | Cotton rib, modal | 160–220 gsm |
| Everyday layer under clothes | Modal, velvet knit, light brushed polyester | 160–240 gsm |
| Outdoor work, fishing, standing in the cold | Fleece-backed polyester | 280–400 gsm |
| Skiing, hiking, winter running | Grid fleece, merino blend | 150–240 gsm |
| Kids | Cotton, modal; brushed for cold days | 160–240 gsm |
Why brushing makes fabric warmer
Brushing, or napping, lifts fibres on the inner face of the knit into a soft pile. The pile traps a layer of still air next to the skin, and still air is what insulates. That is why a brushed 220 gsm fabric feels warmer than an unbrushed fabric of the same weight — and why fleece-backed fabrics, with a much deeper pile, are the warmest of all.
Synthetic or natural when you sweat
Cotton absorbs moisture and holds it. Polyester barely absorbs it and moves it to the outer face to evaporate. Merino absorbs moisture into the fibre while the surface still feels dry, and keeps insulating when damp. For anything active, the choice is polyester or merino; cotton is for rest.
Stretch, fit and shrinkage
Five to ten percent spandex gives thermals the close fit that keeps warm air in and lets one size fit a wider range of bodies. Every fabric we use is heat-set after knitting and brushing to control width and shrinkage, and we wash-test the sample so the size you approve is the size your customer keeps.
Pick two, wear them, decide
Fabric is easier to judge on the body than on paper. Order the same style in two fabrics, wear them for a day, and choose. See MOQ and pricing or go straight to a product: thermal tops, long johns, fleece-lined leggings, base layers, kids thermals.
Frequently asked questions
What is the warmest fabric for thermal underwear?
Among fabrics that are still comfortable next to the skin, fleece-backed polyester at 300 gsm or more is the warmest for standing still in the cold. For active use in the cold, grid fleece or merino blends keep you warmer overall because they stay drier.
Is cotton good for thermal underwear?
For sleeping, lounging and everyday wear, yes — it is breathable and comfortable. For sport or hard work in the cold, no: cotton holds sweat and then cools you. Use polyester or merino for anything active.
What does gsm mean?
Grams per square metre — the weight of the fabric. For thermals, about 150–200 gsm is light, 200–260 gsm is mid-weight and 280 gsm and above is heavy-weight. It is the most useful single number when comparing two thermal fabrics.
Does brushed fabric pill?
Brushed and velvet fabrics can pill with friction over time; how fast depends on the yarn and the finish. We test pilling on the sample fabric and choose finishes that hold up, and we tell you honestly which fabric will pill sooner.
Which fabric sells best on Amazon and marketplaces?
Brushed polyester-spandex sets and fleece-lined leggings: warm, soft, stretchy enough to fit a wide range of bodies, and priced for impulse purchase. Merino sells to a smaller, higher-paying outdoor audience.
Can I get samples of several fabrics?
Yes. Most buyers order the same style in two fabrics and decide after wearing them. Samples take about 7 days.
Get samples in two fabrics
Send the style and your market. Samples in about 7 days.