Fabric comparison
A sleep sack and a pair of pyjamas do the same basic job: they keep a baby covered overnight. The fabric and the cut are what set them apart. Our sleep sacks are made from double-layer muslin cotton, while most pyjamas are cut from a single layer of cotton, a cotton blend, or fleece, so the two behave differently once the room warms up.
By Vanessa & Bob, Epic in Bali · Updated 8 August 2026
| Sleep sack | Pyjamas | |
|---|---|---|
| Fibre & construction | Double-layer muslin cotton with an open, loose weave, pre-washed so it feels soft from the first wear, sewn with flat seams. | Usually a single layer of woven or knit cotton, sometimes blended with polyester or fleece for warmth, cut like a two-piece set or an all-in-one. |
| Breathability | The open weave leaves small gaps in the fabric that let air move through, so heat doesn't build up against the skin. | A tighter single-layer weave or knit moves less air. Lightweight cotton pyjamas still breathe reasonably well; fleece or thicker blends breathe less. |
| Weight & feel | Light on the skin, since two thin layers of muslin still weigh less than most single-layer fabrics, and it drapes loosely instead of clinging. | Weight depends on the fabric. Lightweight cotton pyjamas feel similar to a single layer of muslin, while fleece or brushed cotton feels noticeably heavier and warmer. |
| Hot-weather performance | Built for warm nights: the loose weave and double layer let heat escape while still giving light cover, so a baby is less likely to overheat underneath it. | Lightweight cotton pyjamas can work fine in heat if you skip a blanket over them. Fleece or blended pyjamas hold in more warmth and can feel too hot in a warm room. |
| Softness & durability | Muslin softens more with every wash and keeps its shape over time, though it creases easily. That's just how the loose weave behaves, not a flaw. | Cotton pyjamas also soften with washing. Blended or fleece fabrics tend to hold their texture and resist wrinkling but soften less over time. |
| Best for | A baby who sleeps in a sack instead of under loose blankets, and warm rooms or climates where extra airflow matters. | A baby who's used to sleeping under a blanket or duvet, a cooler room, or a two-piece your baby can also wear and move around in during the day. |
Choose a sleep sack if you want a warm-weather layer that lets air move freely and you don't use loose blankets in the cot.
Choose pyjamas if your baby sleeps under a blanket or duvet, your room runs cool, or you want a two-piece that doubles as daytime wear.