Cotton vs Silk Pajamas: Which Should You Sleep In?

Both are good fabrics to sleep in, and they behave differently enough that the choice comes down to what you want from the fabric. Cotton is a plant fibre with an open weave that lets air move through it. Silk is a smooth protein filament that feels cool the moment it touches skin and weighs almost nothing. Neither one is a lesser version of the other.

The useful comparison is not which fabric is better but which behaviour you are after. Below is what each fibre is, how each handles heat and moisture, what each costs to own, and how to wash them.

What each fibre actually is

Cotton grows on a plant. The fibres are short, roughly two to four centimetres, and they are spun together into yarn. Each fibre is a twisted ribbon with hollow space inside it, and the yarn made from them has air gaps along its whole length.

Silk is made by a silkworm as one continuous filament, often several hundred metres long. Several filaments are reeled together into a single smooth thread. There is no twist, no short ends, and very little air trapped inside the fibre itself.

That structural difference explains almost everything else. One fabric is full of small pockets of air. The other is a solid, even, very fine strand.

How each one handles heat

Silk conducts heat away from the skin quickly on contact. That is why a silk sheet or a silk pajama top feels cold for the first few seconds. The fabric is pulling warmth from your hand faster than your hand replaces it. It is a real and immediate effect, and on a warm evening it is genuinely pleasant.

Cotton does something different. It does not feel cold on contact, but its weave has more open space in it, so air moves through the fabric rather than around it. Across a full night in a warm room, that airflow is what keeps warm air from building up between the fabric and the skin.

So the honest answer to whether silk keeps you cool is: yes, at the moment you put it on, and by a different mechanism than cotton uses. Contact cooling is instant and does not last. Airflow is slower to notice and works for as long as you are wearing it. A tightly woven, heavier silk moves less air than a loose cotton weave does. A very fine, loosely woven silk moves more.

How each one handles moisture

Both fibres absorb water, which puts them in a different category from synthetics. Silk takes in roughly eleven percent of its own weight in moisture before it feels damp. Cotton takes in about eight percent, but cotton keeps taking it in past that point, and it moves water along the yarn rather than holding it in one place.

In practice: silk handles a light amount of moisture very well and starts to feel heavy once it goes past that. Cotton takes longer to feel wet at all, and when it does get wet it dries slowly. If you run warm at night, the open weave matters more than the absorption number. We wrote about that side of it in cooling pajamas for hot sleepers.

Weight, drape and feel

Silk is measured in momme, which is a weight unit. Sleepwear silk is usually 19 to 22 momme. It has a fluid drape that follows the body closely, a soft sheen, and a smooth surface that slides rather than grips. A whole silk set weighs very little.

Cotton is measured in grams per square metre. It has more body. It falls away from the shape underneath rather than tracing it, so a relaxed cut stays relaxed. The surface has texture you can feel, and that texture is the weave doing its work.

If you like the feeling of fabric barely being there, silk gives you that. If you like a bit of weight and a fabric that holds its own shape, cotton gives you that.

At a glance

Care is the part people underestimate

Silk asks for more attention. Hand wash or a delicate cycle in a mesh bag, cool water, a detergent made for protein fibres, no chlorine bleach, no wringing, dry flat away from direct heat and direct sun. Done properly it lasts years. Done in a hot machine wash it will not.

Cotton goes in the machine on cold and comes out fine. It creases, and it shrinks slightly the first time it meets heat, and neither of those is a defect. Both come from the same fibre property that lets it absorb moisture and soften. Our full method is in how to wash cotton pajamas so they stay soft.

This is worth being honest about before you buy. A silk set you are willing to hand wash is a good purchase. A silk set you will end up putting through a normal wash is not, and that is a question about your laundry habits rather than about the fabric.

What about satin?

Satin is a weave, not a fibre. You can weave silk in a satin structure and you can weave polyester in a satin structure, and both will have the same glossy face. A label that says satin without naming a fibre is describing the surface only. If the fibre matters to you, look for the composition line rather than the word satin.

The same applies in reverse to cotton, which we covered against synthetics in cotton vs polyester pajamas.

Which one to buy

• You want a fabric that runs cool on contact and weighs nothing. Silk.
• You want steady airflow across a whole night. Cotton.
• You want to throw it in the machine without thinking. Cotton.
• You want a smooth surface and a fluid drape. Silk.
• You want something that gets softer the longer you own it. Cotton.
• You want the lightest possible thing to travel with. Silk, and it packs small.

What we make

Isla Lune sets are 100% cotton with nothing blended in. We do not make silk, so this comparison is not us arguing for our own fabric over another one. Silk is a fine thing to sleep in and a lot of people prefer it.

We chose cotton for airflow, for machine washing, and because it softens with age instead of holding still. The sets are designed in Victoria, British Columbia and made in small batches. The collection is sold as separates, tops at $48 CAD and pants at $68 CAD, XXS to XXL, in Love Letter, Raspberry and Moonmilk. Shipping is free across Canada and returns are open 30 days on unworn, unwashed items with tags on.

Common questions

Are silk or cotton pajamas better?

Neither, in the abstract. Silk feels cool on contact, weighs very little and drapes close to the body. Cotton moves more air through its weave across a full night, goes in the washing machine, and softens with every wash. Pick based on which of those you notice more, and on how much laundry care you are willing to give a garment.

Do silk pajamas keep you cool?

On contact, yes. Silk conducts heat away from the skin quickly, which is why it feels cold the second you put it on. That effect fades once the fabric matches your temperature. After that, how cool anything keeps you depends on how much air passes through the weave, and a light open cotton weave usually passes more than a heavy silk one.

Are silk pajamas breathable?

Reasonably. Silk absorbs about eleven percent of its weight in moisture, which is more than cotton absorbs before feeling damp. The limit is airflow rather than absorption. Silk is woven from a fine continuous filament with few gaps, so a heavier momme silk moves less air through the fabric than a loosely woven cotton does.

What is the difference between silk and satin pajamas?

Silk is a fibre. Satin is a weave structure that produces a glossy face and a dull back, and it can be woven from silk, polyester, nylon or anything else. Silk satin and polyester satin look similar and behave nothing alike. Read the fibre composition on the label rather than the word on the front.

Are silk pajamas worth it?

They are if you like the way silk feels and you are willing to hand wash or run a delicate cycle. Silk costs more to buy and more to look after, and cared for properly it lasts a long time. If your laundry routine is one machine load on cold, cotton will serve you better for the money.

---

More: cotton vs polyester pajamas, cooling pajamas for hot sleepers, and how to build an evening routine you will actually keep.