Which duvet to choose: filling, cover, weight

In short: the warmth of a bed comes not from the duvet cover but from the filling, while the feel comes from the cover. These are two distinct decisions, and we almost always confuse them. Here's how I make them, weight by weight, material by material - and what sleep research confirms, or doesn't.

Every year around the same time, I get asked the same question, phrased incorrectly: “Which silk duvet for winter?” The instinct is understandable. Yet it conflates two things that have neither the same function, nor the same material, nor the same price: the duvet, which is filling enclosed in a shell, and the duvet cover, which is a woven textile. The first determines warmth. The second determines everything else - the feel, the smoothness, the way moisture is wicked away.

This confusion is costly. You buy a beautiful duvet cover hoping to feel less cold, and you're still cold. Or the opposite: a 6 kg duvet under a scratchy cover, and you sweat without ever finding comfort. Let's start from the beginning.

The filling: the only thing that creates warmth

A duvet doesn't generate heat. It traps the air your body has warmed and keeps it from escaping. That's the whole art: obtaining lots of still air with as little material as possible. This is called fill power.

The three types of filling behave very differently:

Long-fiber silk - the kind that fills our duvets - works on a different principle from down. Where down creates loft, silk creates drape: the duvet conforms to the body, leaving less empty space to warm, and far fewer drafts when you turn over. That's why a silk duvet can feel warm sooner even though it looks thinner.

What the research says (and what it does not say)

I prefer to be frank about the state of knowledge. A systematic review published in 2024 in the Journal of Sleep Research (Li, Halaki & Chow, How do sleepwear and bedding fibre types affect sleep quality, 33(6), PMID 38627879) brought together the nine available trials comparing bedding and sleepwear fibres. Its findings: in cold conditions, duvets filled with down were associated with more deep sleep; wool made it easier to fall asleep in the cold; linen improved sleep quality in warm conditions among young adults.

Silk filling does not appear in these trials. In other words: nothing contradicts it, but nothing proves it either. The authors also point out that the protocols are too heterogeneous to draw clear conclusions between fibres, and call for standardised methodologies. The strongest finding is the general principle: the bed microclimate — the temperature and humidity between the body and the textile — genuinely affects the night. Choosing the material is one way to influence it, not a promise.

Weight: the real question for winter

Once you have chosen the filling, everything comes down to the filling weight. Our duvets are ordered by weight, and this is where most people get it wrong — almost always by choosing too much.

Only two parameters matter: the actual temperature in your room and your own thermostat. French energy-saving recommendations put the bedroom temperature at around 17°C; many homes are actually at 19 or 20°C, and a duvet designed for 17°C becomes suffocatingly hot there.

• Room at 19-20°C, you tend to feel hot at night — keep it light: 1 to 2 kg in 200×200, 2.5 to 3 kg in 240×260. This is the choice for sleepers who throw the duvet off around 3 a.m.
• Room at 17-18°C, average sensitivity — the comfortable range: 2.5 to 3.5 kg in 200×200, 4 to 4.5 kg in 240×260.
• Room at 16°C or below, or if you feel the cold easily — 4 kg and more in 200×200, up to 5.5 or 6 kg in larger sizes.
• Shared bed, opposite thermostat preferences - choose the weight suited to the person who feels the coldest and let the other adjust with the flat sheet and pajamas. It is simpler than negotiating over the duvet.

A practical rule of thumb: the right duvet is the one you keep over you all night without thinking about it. If you push it away, it is too heavy. If you curl up, it is too light. Neither can be fixed by changing the cover.

The cover: the only material your skin touches

The cover barely adds any warmth. It determines the feel - and how the water vapor you produce at night leaves the bed. In this respect, the materials are not at all equal.

Momme (MM) measures the density of silk, not its quality: it is the unit that explains why a 22 MM cover does not drape like a 19 MM one. If the term is unfamiliar, I have devoted an entire guide to it: momme, the unit that changes everything when buying silk. All the materials above can be found in our duvet covers.

Three mistakes I keep seeing

1. Increase the weight rather than the peripheral insulation. Heat loss occurs at the sides, not through the top. A duvet with the right width - 240×260 on a 160 cm bed - does more than adding 500 g of filling.
2. Keep the same duvet all year without adjusting anything. A so-called all-season duvet doesn't cancel out the seasons: it lets you adjust what's underneath. Simply changing the flat sheet according to the month is often enough, and I explain the reasoning in detail in this article on layering in winter.
3. Choose the cover before the duvet. This is the opposite order to what thermal logic would suggest, and yet it is the most common.

Care: what really extends a duvet's life

A silk or down duvet should not be machine-washed: dry cleaning is the recommended option, and it remains infrequent - once a year is enough in most households, because the cover absorbs most of the wear. The daily habit that matters is more modest: air the duvet spread out for twenty minutes in the morning, with the window slightly open, to release the night's moisture before making the bed. This is what preserves its loft, far more than any washing.

Frequently asked questions

Does a silk duvet keep you warm in winter?

Yes, provided you choose the right weight. Silk insulates through contact rather than volume: it feels thin but limits drafts. In a room at 17-18 °C, allow 2.5 to 3.5 kg in 200×200.

What duvet weight for a room heated to 20 °C?

Keep it light: 1 to 2 kg in 200×200 is more than enough. Beyond that, most sleepers end up uncovering themselves during the night, which affects sleep more than being slightly too cool.

Do you need a silk cover for a silk duvet?

It is not mandatory. Choose the cover based on the feel you want and how much you sweat at night, not on the filling. A silk duvet under a linen cover is a very coherent pairing.

Can you wash a silk duvet at home?

No. Machine washing disrupts the quilting and breaks the long fibers. Dry cleaning, with regular airing in between.

What duvet size for a 160 cm bed?

240×260 cm. The side overhang is what keeps you warm at the sides - it is the most underestimated factor in all winter bedding.

To go further

If you remember only one thing: choose the weight first, and only then the material you will touch. The two decisions are made separately, and in that order. Our silk duvets are ordered by size and weight, and pair with the entire Studio bedding collection.

— Colette, for the StudioSoie Journal