What Does "Dress Baby in Natural, Breathable Fibres" Actually Mean?

Every parent hears it from various trusted sources: dress your baby in natural, breathable fibres. Sensible advice. But what exactly are those fibres and why does it matter so much?

Let’s start with thermoregulation.

Babies and Thermoregulation: A Work in Progress

A healthy body temperature sits between 36.5°C and 37.5°C. Adults manage this automatically, we shiver, sweat, change blood flow, adjust our breathing and muscle tone. Much of it happens quietly, without us noticing.

Babies, however, are still physically developing.

Most infants will have reliable thermoregulation between six and twelve months. Before that, their systems are immature. They can’t shiver effectively. They have a high surface-area-to-body-mass ratio, meaning they lose heat quickly. They use a special type of fat, brown fat, to generate warmth, but it costs energy. A lot of energy.

And babies can’t tell us when or why they’re uncomfortable.

If a baby overheats, they burn precious calories trying to cool down. If they get cold, they burn calories trying to warm up. Those calories should be used for growth, brain development and immune strength, not temperature battles.

This isn’t dramatic; it’s physiological reality. Dehydration can occur within hours. Hypothermia in newborns can develop frighteningly quickly, particularly in the first 72 hours of life. Maintaining a stable temperature is not just comfort, it’s safety.

Two factors matter most:

1. The environment.
2. What your baby is wearing.

Today, we’re talking about what your baby is wearing and wrapped in.

“Natural and Breathable” Decoded

I have a degree in clothing and textile science, and at the heart of it all was a deep respect for natural fibres. They are complex, clever and, in most cases, unmatched by synthetics or manmade fibres.

Let’s build confidence around what counts.

Cotton ✔ Natural

Cotton is a plant fibre. Lightweight. Widely available. Generally breathable.

But cotton holds onto moisture. Think about your washing, cotton stays wet longer. On a baby, damp fabric in a cool room draws heat away from the body. It also takes multiple layers to provide warmth because structurally, cotton fibres are relatively flat.

Cotton is great in many situations. But it has limits.

Bamboo ✘ Not Truly Natural

Bamboo sounds wholesome. It isn’t, in textile terms.

To turn bamboo into fabric, it undergoes heavy chemical processing. The result is typically viscose or rayon which is a regenerated fibre. It’s not allowed to be marketed as a true natural fibre in many jurisdictions because of this transformation.

The processing alters breathability and moisture behaviour. While soft, it does not function like wool in managing temperature. “Natural” branding can be misleading here.

Wool ✔ Natural

All sheep’s wool is natural and breathable. Wool fibres are crimped and three-dimensional, trapping air for insulation while allowing moisture vapour to pass through. That dual function, insulation and ventilation, is rare and it’s the magic sauce.

Merino Wool ✔ Natural (and Exceptional)

From the Merino sheep, merino wool is finer, softer and remarkably effective at thermoregulation. Over fifteen academic studies demonstrate its ability to buffer temperature and manage moisture.

Merino can absorb up to around 30% of its weight in moisture vapour without feeling wet. It draws moisture away from the skin, releases it into the air and helps maintain a stable microclimate around the body.

In simple terms: it works with your baby’s physiology rather than against it.

It is warm in winter. Breathable in mild weather. Quick drying. Naturally antibacterial. And gentle enough for newborn skin.

Lambswool ✔ Natural

Wool from young sheep. Soft and warm. A lovely option, though sometimes pricier.

Silk ✔ Natural

Produced by silkworms. Breathable and thermoregulating, though less commonly available for babywear in the UK.

Linen ✔ Natural

Made from flax. Breathable and strong, but can feel coarse for delicate baby skin.

Muslin ✔ (Because It’s Usually 100% Cotton)

Muslin refers to the weave, not the fibre. If it’s cotton muslin, it’s cotton.

Fleece ✘ Usually Synthetic

Fleece describes a fabric structure. Most fleece is polyester — petroleum-derived plastic. It traps heat but does not manage moisture vapour well. If it’s labelled 100% wool fleece, that’s different. Check carefully.

Cashmere ✔ Natural

From cashmere goats. Soft, breathable and insulating. Expensive.

Polyester ✘ Synthetic

Made from petroleum. Used widely in baby clothing: pram suits, snow suits, dress-up costumes, blended bodysuits. Breathability depends on construction, but fundamentally it does not behave like wool.

Plastic-based fibres can trap moisture. When moisture cannot move away from the skin efficiently, overheating risk increases.

Why Fibre Choice Matters

Babies get wet. They dribble, they’re sick, nappies leak. Cotton absorbs liquid and stays wet. In a cool room, that wetness pulls warmth from the body.

Merino wool behaves differently. It manages moisture vapour, dries faster and continues insulating even when damp. It is also naturally antibacterial, meaning it doesn’t require washing after every minor spill, unlike cotton.

Care is simple: cool wash, no hot water, no tumble dryer (but remember it dries quickly compared to cotton).

The Pram Suit Problem

Many newborn wardrobes are filled with polyester pram suits and fleece layers. They look cosy. In snow, layered over merino in Nordic climates, they serve a purpose.

But in a 19°C British winter room? Or in a car seat or warm pram? They can easily lead to overheating.

If your baby wears a synthetic Halloween costume, enjoy the photos, briefly, in a cool room. Then change them. Their temperature stability matters more than aesthetics.

A Simple, Science-Based Approach

For clarity, guidance could simply say:

Dress baby in 100% natural fibres — primarily cotton and wool. Avoid blends. Avoid synthetic fleece for routine wear.

Better still:

• Use 100% merino wool against the skin.
• Layer with merino or other wool.
• Add cotton if needed.
• Adjust layers rather than switching to synthetics.

Kiwi parents have long embraced merino layers and bedding. It’s quietly practical.

But What About Cost?

Merino isn’t yet common in UK supermarkets or the high street. But it is available online. And second-hand.

It is durable. Shareable. Resellable. Much of my own children’s merino came to us third or fourth hand and has already been through at least one more baby.

I cannot say that for cotton onesies, even the ones that cost as much as if they were merino.

Fewer, better items often cost less in the long run.

This Isn’t About Fear

It’s about informed choices.

The reality is this:

• Dehydration from overheating can develop within hours.
• Hypothermia in newborns can develop rapidly, particularly in the first days of life.

Those extremes are rare but importantly, they’re preventable.

A beautifully simple prevention strategy exists:

Dress your baby only in 100% natural fibres. Cotton. Wool. Merino wool. No confusing blends. No petroleum-based fillers. No unnecessary layers.

Warm. Breathable. Stable.

For caregivers wired to worry about every detail, that simplicity brings profound peace of mind.

And, for me, peace of mind is the most valuable layer of all.