Duvet shopping is full of jargon that nobody bothers to explain. This page does. Skim the chart first to see how warmth and weight line up, then use the glossary below to decode anything on a label. Where a term links out, that is to the full guide on it.
Estimated tog to GSM chart, by filling
GSM only tells you about warmth once you know the filling, because down traps far more heat per gram than synthetic. So the same tog needs very different weights depending on what is inside. These are TogWise estimates from the same model as our converter, not measurements of real duvets. Use them as a rough guide, and trust the product's own label over this chart.
| Tog | Down | Feather & down | Microfibre | Hollowfibre | Best for |
|---|---|---|---|---|---|
| 4.5 | 65-80 | 105-130 | 150-190 | 165-210 | Summer |
| 7 | 100-125 | 160-205 | 235-300 | 260-330 | Late spring |
| 9 | 125-160 | 205-260 | 300-385 | 335-425 | Spring, autumn |
| 10.5 | 150-190 | 240-305 | 350-445 | 390-495 | Spring, autumn |
| 13.5 | 190-240 | 310-395 | 450-575 | 500-635 | Winter |
| 15 | 210-270 | 345-435 | 500-640 | 555-705 | Deep winter |
Figures are estimated GSM (grams per square metre), not measured values. Fill power, brand and construction can all shift them. To convert a specific number, use our tog to GSM converter.
Warmth and weight
Tog. A measure of how well a duvet traps your body heat. UK duvets run from about 1 tog (cool and light, for summer) up to 15 tog (very warm, for a cold winter room). Higher means warmer. Full detail is in what is a tog rating.
GSM (grams per square metre). The weight of filling packed into each square metre of the duvet. More GSM is usually warmer, but only when you compare the same filling, because some fillings trap far more heat per gram than others.
Fill power. How much space a given weight of down takes up. Higher fill power down is fluffier, so it is warmer for its weight and the duvet can feel light and still keep you toasty. It is the reason a good down duvet costs more. There is more in down vs synthetic.
Fill weight. The total weight of filling inside the duvet, usually quoted in grams. Divide it across the duvet's size and you are close to the GSM.
Fillings
Down. The soft, three-dimensional clusters from under a duck or goose's outer feathers. It is the warmest filling for its weight, the most breathable, and usually the most expensive. Goose down tends to be a touch warmer than duck.
Feather. The flatter, quill-bearing plumage. Heavier and less insulating than down, and it can poke through the cover, so it is almost always blended with down rather than used alone.
Down and feather blend. A mix, labelled by ratio such as 70/30. More down means lighter and warmer, more feather means cheaper and heavier.
Microfibre. A very fine synthetic fibre spun to behave a bit like down. Soft, machine washable, kind to allergies and far cheaper, though heavier for the same warmth.
Hollowfibre. A thicker synthetic fibre with a hollow core that traps air. Springy and hard-wearing, the most budget-friendly filling, and the heaviest for a given tog.
Construction
Baffle box. Internal fabric walls that form boxes and let the filling loft fully without sliding around. You find it in better down duvets, and it is why they look so plump.
Box stitch. Squares stitched straight through the duvet to hold the filling in place. Cheaper than baffle box, but the stitched lines can feel slightly cooler.
All-seasons duvet (3-in-1). Two duvets, usually a lighter one around 4.5 tog and a medium one around 9 tog, that popper together into roughly 13.5 tog for winter and come apart for warmer months. One of the best-value ways to cover the whole year, covered in best tog duvet for winter. Our combine two duvets calculator adds any two togs together.
Corner ties. Small loops at the corners that hold the duvet inside its cover so it cannot slide into a lump at the bottom.
Fabric and finish
Thread count. The number of threads woven into a square inch of the cover fabric. Higher can feel smoother, but beyond a point it adds price more than comfort. The full story is in thread count explained.
Percale. A crisp, matte weave with a cool, fresh, hotel-sheet feel. Good if you sleep warm.
Sateen. A smoother, slightly lustrous weave that feels warmer and more luxurious against the skin.
Labels and standards
Oeko-Tex Standard 100. A label meaning the fabric has been tested for harmful substances. Reassuring for sensitive skin and for baby bedding.
Responsible Down Standard (RDS). Certifies the down was sourced without live-plucking or force-feeding. Worth looking for on any down duvet.
Anti-allergy. A finish or a tightly woven cover that limits dust mites. Helpful if you have allergies, though no duvet is completely allergen-proof.