What Should Babies Wear to Bed in Autumn?

Baby sleeping bags are now firmly on the newborn essentials list in the United Kingdom. They’re easy to get on and off, they can’t be kicked off in the middle of the night and, when properly fitted and used according to safe sleep guidance, they remove the need for loose, potentially dangerous, bedding.

Most of the sleeping bags you’ll see follow a very similar formula: a cotton or viscose (that's often called bamboo) outer layer, polyester padding on the inside and a TOG number on the label. The packaging often gives you some guidance on layering underneath too. But I've heard plenty of parents ask about natural fibre alternatives and say this formula can be confusing, and feel too prescriptive. 

There is nothing wrong with these sleeping bags and you should always follow safe sleep advice from your local authority. But there is a natural fibre option that meets all the safe sleep guidance too. One that's used (and loved!) in so many other parts of the world!

A 100% merino wool baby sleeping bag uses the natural properties of the fibre to provide warmth, breathability and moisture management. They're soft, don't need washing unless they're grubby and cost about the same or sometimes less than as Organic cotton or bamboo viscose sleeping bags (pretending to be natural!) 

As a Kiwi mum and clothing and textile scientist, I can't recommend 100% merino wool sleeping bags more. So, what makes a merino sleeping bag different?

First: what is merino wool?

Merino is wool from the Merino breed of sheep. Good-quality, superfine merino is dramatically softer than the traditional wool jumpers many of us grew up associating with the word “wool”. Fine merino can sit comfortably directly against the skin and feels much more like a soft jersey fabric.

Our Babu baby sleeping bags also guaranteed non-mulesing, hold Woolmark and OEKO-TEX® Standard 100 certified (chef's kiss for animal welfare, quality and free from harmful levels of toxic chemicals).

But other merino wool sleeping bags, including ones with cotton outer casing, are also great! They just might not have all the bells and whistles ours do...

Merino manages temperature rather than simply trapping warmth

The purpose of insulation is normally straightforward: trap warm air close to the body. With babies we need to be more careful with this as they develop their thermal systems and overheating can be dangerous, especially when they sleep.

Merino is an incredible natural insulator, keeping air still and warm around the body in many different ways, but wool is also remarkably good at managing the little microclimate between our skin and our clothing. Merino fibres can also absorb water vapour before it turns into liquid moisture, moving humidity away from the skin while still feeling dry. At the same time, the fabric remains comfortable, not clammy.

In normal-parent language? Warm without needing to feel heavily padded. Cosy without that clammy, sweaty feeling you can get wearing synthetic layers. That is useful for everyone, but particularly relevant to babies because their thermoregulation is still developing.

It also makes merino particularly useful in autumn British homes, where a bedroom might be 22°C when you put your baby to bed and considerably cooler at 4am. There are always those few weeks when you've not got the heating on or it's just starting and it takes a while to get right... merino is especially great during this time!

So where is the TOG rating?

Thermal Overall Grade (TOG) measures thermal resistance: essentially how much insulation a product provides under standardised conditions. For passive fibres, like cotton, polyester, and bamboo viscose, they're great because they behave the same way all the time. 

Wool is an active fibre, it adapts to the microclimate around skin and managing any moisture (which has a surprisingly big impact on how comfortable you are wearing it). 

Instead of TOG ratings, merino sleeping bags are described using fabric weight, season or recommended room-temperature ranges. Merino wool with cotton sleeping bags are less insulating then double-jersey merino sleeping bags and the weight of the merino can differ - so there are of course differences however because the fibre will adapt somewhat, they don't need to be as prescriptive as TOG ratings.

A merino sleeping bag can respond to changes in heat and humidity around the body in ways that a fixed layer of polyester wadding simply cannot. I realise some people like a prescription but they can also be confusing if it doesn't feel right - if the 20 degree room feels too hot to be using a certain TOG rated sleeping bag and specific layers underneath. Merino wool sleeping bags can give you more peace of mind in this instance, knowing the fabric will adapt and simply keep your baby comfortable throughout reasonable temperature changes during the night.

One sleeping bag can cover a surprisingly large chunk of the year

This is probably my favourite practical advantage of merino wool. Instead of owning several sleeping bags for each season, an All-seasons 100% merino baby sleeping bag can be used most of the year by changing what your baby wears underneath it.

Warmer evening? A lightweight bodysuit. Cooler night? Long sleeves or a merino onesie underneath.

That ability to layer is one reason merino sleeping bags have been such a staple in New Zealand homes. It’s also incredibly useful for travel, staying with grandparents (who either have the heating on too hot or too cold, why?!), camping or anywhere else where you don’t have as much control over the temperature and environment.

The washing hack

If you’ve already used merino wool clothing, you’ll know this is one of its greatest parenting superpowers. Wool is naturally excellent at managing moisture and odour, which means it generally doesn’t need to be washed simply because it has been slept in.

Obviously baby sick, exploding nappies and breakfast have other ideas. But under normal use, airing a merino sleeping bag between sleeps, just over the side of the cot, is often all it needs. And when disaster strikes, let's not forget it's not the first time that wool has been exposed to the elements! When it was on the sheep it managed everything and most of the time it can still do that. Just follow the washing instructions on the tag.

Less washing means less work and cost saved, but it also matters to the life of the garment. Every wash creates mechanical stress on fibres, seams, zips and trims. A garment that can be washed less frequently has a very good chance of lasting longer. 

And yes, they are made to last

There is sometimes an assumption that because fine merino feels delicate, it must be delicate. Nope, not necessarily. Merino is a fine fibre, so it deserves sensible care, but good-quality knitted merino babywear can have an extremely long, useful life.

The key is washing it correctly: use a wool or delicate cycle, a suitable wool detergent if you can, close zips before washing and air dry flat. It will dry quicker than cotton, in a few hours on a mild day and usually overnight on a drying rack.

Treat it properly and a merino sleeping bag can move from one baby to another, be passed through siblings and then still have plenty of life left for resale or handing on. That is also why good merino tends to have a healthy second-hand life. 

Are merino sleeping bags expensive?

Compared with an entry-level, polyester-filled, sleeping bag from a supermarket? Yes. Our 100% merino sleeping bags are £73 (September 2026). This is the same price as other Bamboo Viscose and Organic Cotton, polyester-filled sleeping bags and about 30% cheaper than other sleeping bags again, only using bamboo and cotton. However, with merino wool, they are naturally warm, you don't need as many and you don't wash them as often.

I had two passed on from a friend that saw us through about three years, all year round. Airing them over the side of the cot every day meant I washed them as little as I could and I'm just about to pass them on for friends to use - these will be the fifth children the bags will be going through and, honestly, they still look and feel new.

If it becomes the sleeping bag you reach for night after night, across several seasons, on holidays and at grandparents’ houses then eventually gets passed to another child or sold on, its cost per wear starts looking very different.

That, to me, is where buying better baby clothing makes sense. Not because babies need wardrobes full of expensive things. Quite the opposite. They need a small number of really reliable things that work hard. And a 100% merino wool sleeping bag is exactly that sort of piece.