Is a wool mattress warm in winter?

In September we wrote about why natural mattresses sleep cooler in summer. The same question now comes back in reverse: if wool keeps you cool in August, will it leave you cold in January?

It will not. The reason is the same in both seasons, and it is worth understanding before you pile on another blanket.

What wool does that foam does not

Wool does not work like a heater. It does not add warmth of its own. What it does is manage the air and moisture around you.

• It holds still air. Wool fibres are naturally crimped, so a layer of wool traps small pockets of air. Still air is a good insulator, which is why a wool layer feels warm without feeling heavy.
• It handles moisture. You lose moisture through the night in every season. Wool can take up a good deal of moisture vapour before it feels damp, so the bed stays drier. A dry bed feels warmer than a damp one.

That is the same reason a natural mattress feels cooler in summer: the heat and moisture have somewhere to go, so they do not build up around you. In our summer article we called it trapped heat. In winter, the risk is the opposite: a clammy chill once the heating goes off.

What the research does and does not show

We would rather be careful here than sell you a promise.

A 2016 study in Nature and Science of Sleep (Shin and colleagues) tested 17 young adults sleeping in rooms at 17°C and 22°C. People fell asleep faster when they wore wool sleepwear. When the researchers changed the bedding instead, they found no effect on sleep. The study was funded by the wool industry, and it was small.

So the fair reading is this: wool next to the skin may help some people settle on a cool night. Nobody has shown that a wool mattress, on its own, makes you sleep better. What wool reliably does is regulate temperature. That is the quality to buy it for.

What this looks like in a real bed

Several of the makers on our floor build with natural fillings. Our own Westend beds are filled with hand-teased horsehair, lambswool, cotton and silk. Marshall & Stewart beds use horsehair, wool, cashmere, cotton and flax. Hypnos makes a Wool Origins collection. In each, the natural layers sit between you and the springs, so the air around you can move.

A mattress built mostly from foam behaves differently. It tends to hold the heat you give it, which can feel cosy at first and sticky by three in the morning. That is a generalisation, not a rule, and some people sleep beautifully on foam. If you run hot in summer and cold in winter, natural fillings are worth trying first.

Layering a bed for a cold room

Your mattress is only the bottom layer. On a cold night, the layers above it do most of the work.

• A wool topper. If your mattress is firm or your room is cold, a wool topper adds a soft, insulating layer under you. Heat lost downwards is easy to forget.
• The right duvet. Down, silk, camel hair and cashmere each feel different. Our duvets come in any size, including bespoke. We will cover tog ratings in December.
• Sheets that suit you. Cotton sateen feels smoother and a little warmer to the touch than crisp percale. Pure linen breathes freely all year. Our bed linen comes in all three.
• A throw at the foot. It is easier to add a light layer at 2am than to swap a duvet.

Three things you can do tonight

• Turn the heating down, not up. A cool room with a well-layered bed usually sleeps better than a warm room with a heavy duvet.
• Air the bed in the morning. Pull the covers back for half an hour so moisture can leave the mattress.
• Add underneath before you add on top. A topper or an extra layer under the sheet often fixes "cold" faster than another blanket.

Frequently asked questions

Is a wool mattress warm in winter?

Yes. Wool traps still air and handles moisture, so a wool-filled mattress feels warm and dry on a cold night without overheating you. It regulates temperature rather than adding heat.

Does a wool mattress get too hot in summer?

Not usually. The same qualities that keep it comfortable in winter let heat and moisture escape in summer. We explain this in our guide to why natural mattresses sleep cooler in summer.

Does sleeping on wool help you sleep better?

One small, industry-funded study found people fell asleep faster in wool sleepwear, but found no effect from changing the bedding. Buy wool for comfort and temperature control, not as a sleep cure.