What Should a Baby Wear Under a Swaddle?

A two-pack of bamboo muslin swaddles rolled together, one rust brown and one printed with carousel horses

This is a question about temperature, and it's one of the few places where a fabric decision is a safety decision. I write the specification for these, so I'll be direct. One thin layer. In a warm bedroom, often nothing beyond the nappy. Here's the bit almost everybody misses: the swaddle is a layer. A muslin feels like nothing at all in your hand and behaves like a full layer the moment it goes twice round a torso, and she can't do anything about your answer, no kicking a blanket off, no pushing an arm out of a sleeve, no squirming to a cooler patch of mattress.

Whatever you dressed her in an hour ago is what she's got. That's what makes this a safety question.

By room temperature

The swaddle itself is a layer. Every number below already counts it, which is where most overdressing starts.

Under-swaddle layers for a single bamboo muslin wrap
Room	Under the swaddle	Notes
29-31°C, no air-con	Nappy only	Consider skipping the wrap on the hottest nights
27-28°C, fan only	Nappy, or a sleeveless bodysuit	Watch the back of the neck for dampness
25-26°C, air-con	Short-sleeve cotton or bamboo bodysuit	The most common Singapore bedroom
23-24°C, air-con high	Long-sleeve bodysuit	Rare here; raise the thermostat instead if you can
Any	No hat indoors	Babies lose heat through the head: leave it uncovered

Elsewhere the rule is one more layer than an adult. Here it is about the same as an adult, or one fewer.

How to tell she is too warm

Two fingers on the back of her neck, or a hand on her chest between the shoulder blades.

Warm and dry is right. Damp, clammy or hot means one layer too many.

Don't judge by her hands or feet. They run cool in almost every baby and aren't a temperature signal.
A flushed face, damp hair at the nape, or rapid breathing during sleep all point the same way.
Heat rash on the neck, chest or back of the shoulders is the delayed version of the same message.
If she has escaped the wrap and calmed down immediately, take that as data.

If heat is the problem

Does the swaddle fabric change the answer?

A good deal. An open bamboo muslin weave moves air and takes moisture away from the skin. A jersey wrap, a double-layer cotton or anything quilted keeps both. Two wraps described identically on a label can behave a full layer apart on a humid night.

This is the reason I specify bamboo for our swaddles, and say so at every opportunity. In a climate where the fabric is doing the temperature regulation the baby can't do herself, the weave isn't a comfort preference.

Mentioned above

Bamboo Swaddles (3pc)S$69.00Shop now

Bamboo Swaddle Single (Solid Colours)S$26.00Shop now

On fabric

What she should never wear under one

Short list, and every item on it is on it for the same reason: overheating.

A hat, indoors. Head covering plus a wrap is a well-established overheating combination.
Fleece, wool or anything padded. There's no bedroom in this country that calls for it.
A second swaddle over the first. If she seems cold, raise the room temperature and don't add layers she can't remove.
A sleep sack under or over the wrap. Choose one format, not both.
Anything with a hood, ties, ribbons or loose fastenings that could ride up toward her face.

Once the swaddling weeks are over the same logic carries into the sleep sack, with TOG doing the arithmetic for you. We've written the sleepwear question out in full for both stages, including what changes when the air-con goes off at 6am and the room climbs eight degrees before she wakes. Eight is our measurement. I'm not certain it's yours.

Evidence

This guide is general information, written to help you understand a topic and ask better questions. It is not medical advice and does not replace your own doctor, midwife or paediatrician. Anything that worries you about your baby belongs with them.

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