Why what you sleep in changes how you sleep.
Most sleepwear is made from cotton or polyester. Both are perfectly good fabrics. Neither is good at the specific job of keeping you comfortable when you get warm in the night.
The problem with cotton
Cotton is absorbent, and that sounds like a virtue. It is, up to a point. Cotton fibres soak up moisture and hold onto it inside the fibre itself. Once a cotton top has taken on moisture it stays damp, and damp fabric sitting against skin is what makes you feel cold and clammy an hour after you were too hot. Cotton is slow to release what it has absorbed, so the cycle takes a long time to break.
The problem with polyester
Polyester goes the other way. It barely absorbs anything, which is why sportswear uses it. But most sleepwear polyester is knitted densely and finished smooth, and the result traps a layer of warm air against the skin with nowhere for heat to go. It moves moisture along the surface but does not let warmth escape.
What we use instead
Cool Bloom sleepwear is made from bamboo viscose, blended with a small amount of elastane for movement and recovery.
Bamboo viscose is a regenerated cellulose fibre. In practical terms that means it behaves differently from both of the above in three ways that matter at three in the morning:
- It wicks, then releases. The fibre moves moisture away from the skin and out to the surface of the fabric, where it evaporates into the air. It does not lock it inside the fibre the way cotton does. Less time damp means less of the hot-then-cold swing.
- It breathes. The yarn is spun and knitted to sit fluidly rather than tightly, so warm air moves out through the fabric rather than pooling against you.
- It stays smooth. The fibre surface is round and low-friction, so it drapes away from the body instead of clinging when you are warm.
How the three compare
| Cotton | Polyester | Bamboo viscose | |
|---|---|---|---|
| Absorbs moisture | Yes, and holds it | Barely | Yes, and releases it |
| Dries quickly | Slowly | Quickly | Quickly |
| Lets heat escape | Moderately | Poorly | Well |
| Feel against warm skin | Becomes heavy | Can feel slick | Stays light and dry |
Our specification
We hold every Cool Bloom garment to the same spec:
- 95% bamboo viscose, 5% elastane for the sleepwear
- 100% bamboo viscose for the pillowcases
- Flat seams, no scratchy labels, envelope closures rather than buttons
Looking after it
Bamboo viscose is easy to live with, but it does not like heat or fabric softener. Machine wash cool, line dry or tumble on low, and skip the softener entirely. Softener coats the fibre and is the single fastest way to undo the wicking you paid for.
A note on what this page does not say: we make no medical claims for our fabric. Cool Bloom sleepwear is designed to be comfortable and breathable. It is clothing, not treatment.