TOG rating for a baby sleeping bag: what it means—and when you don’t need to pay attention to it
You’re standing in a baby store or scrolling through an online shop, and it’s everywhere: 1.0 TOG. 2.5 TOG. 3.5 TOG. Summer, transitional season, winter.
And you’re thinking: how many sleep sacks do I actually need here?
It’s one of the most frequently asked questions I receive. Not because parents don’t understand it—but because the system itself is confusing. You buy something for your baby’s night, and you have to do a calculation as well.
Let’s take it apart calmly.
What TOG actually means
TOG stands for Thermal Overall Grade. It measures insulation: how much heat does a fabric retain?
The higher the number, the more insulation. A lightweight summer sleep sack is around 0.5 TOG. A thick winter sleep sack is around 2.5 to 3.5 TOG.
Important to know: TOG says something about the fabric, not your baby. It’s a fixed number measured in a laboratory. It doesn’t adapt to anything. Whether it’s a cool night or a sweltering one, the sleep sack does exactly the same thing.
That’s exactly where the problem lies.
Why TOG is so complicated in practice
The TOG system assumes that you know and combine three things:
- The bedroom temperature—which changes during the night
- The sleep sack’s TOG rating
- The layers underneath, which also have a TOG rating
A bodysuit counts. A sleepsuit counts. A sheet counts. You have to add them all together and arrive at something suitable for the room temperature at that moment.
The guideline looks roughly like this:
| Room temperature | Total insulation, approximately |
|---|---|
| below 16 °C | 4.0 TOG |
| 16–19 °C | 2.5 TOG |
| 20–22 °C | 2.0 TOG |
| 23–25 °C | 1.0 TOG |
| above 26 °C | 0.5 TOG |
On paper, that’s clear. In practice, at 11:15 p.m., you’re standing there with a thermometer in your hand, wondering whether 19.5 °C should be rounded up or down.
And here’s the real issue: a Dutch bedroom rarely stays in the same category all year round. A room that is 17 degrees in February is 24 degrees in July. According to this system, you therefore need at least two, and often three, sleep sacks. In each size. And your baby grows.
What I saw in the neonatal unit
In my 28 years at the bedside of newborns, almost everything revolved around temperature.
A newborn baby cannot yet retain or release its own body heat effectively. The system that regulates this is in place, but it is still immature. A baby who is too cold uses energy to stay warm — energy they need to grow. A baby who is too warm becomes restless, clammy, and sleeps for shorter periods.
What has always stayed with me is this: it’s not about being warm enough. It’s about being stable. A baby who remains at roughly the same level of comfort throughout the night sleeps more peacefully than a baby who suddenly becomes too warm at three in the morning.
And that’s precisely what a fixed TOG rating can’t provide. It’s one setting for a night that changes.
Why merino wool doesn’t need a TOG rating
Wool works fundamentally differently from cotton or polyester.
The merino fibre is hollow and crimped. This allows it to trap air — that’s the insulation. But the fibre also absorbs moisture, up to a considerable proportion of its own weight, without feeling wet. And when it gets warmer, it releases that moisture back into the air.
Releasing moisture takes heat. The result: when your baby gets warmer, the wool wicks away moisture and heat. When it cools down, the fibre structure traps air again and insulates.
The material therefore responds to the conditions instead of offering one fixed answer.
That’s why our sleep sacks don’t have a TOG rating. Not because we forgot to add one, but because the number isn’t a good fit. One merino wool sleep sack works in a 17-degree room in January and in the same room at 23 degrees in June.
Let’s be honest: wool isn’t a thermostat and it doesn’t take away your responsibility to supervise. In extreme heat, dress your baby in lighter clothing under the sleep sack — exactly as you would dress yourself. The difference is that you don’t need to change sleep sacks.
The check that’s more reliable than any number
Want to know whether your baby is comfortable? Place your hand on the back of their neck, between the shoulder blades.
- Comfortably warm — just right
- Clammy or sweaty — remove a layer
- Cool — add a layer
Don’t feel their hands or feet. Babies’ hands and feet are almost always cooler, even when the rest of their body is perfectly warm. That’s normal circulation, not a signal.
This neck check takes five seconds and tells you more than any chart. It’s the only measurement that takes your baby, in your room, at this moment into account.
What remains of TOG?
TOG is not nonsense. For a synthetic or cotton sleeping bag, it is useful information—you at least know what you are getting.
But it is a tool for materials that do not adapt themselves. As soon as you work with wool, the question shifts. No longer which number is right for which month, but: does this fit well, is it breathable, and does my baby’s neck feel comfortable?
That is much calmer. And calm is exactly what you are looking for at night.
Frequently asked questions
Does a merino wool sleeping bag really have no TOG rating?
That’s right. TOG measures fixed insulation and does not take moisture regulation into account. Because merino wool responds to moisture by releasing it, one fixed number is not representative. We therefore prefer to explain how the material works rather than give a figure that tells only half the story.
Can’t my baby get too warm in wool, then?
Wool wicks away moisture and heat, which helps prevent overheating. But at high room temperatures, always dress your baby more lightly under the sleeping bag—a nappy and a thin bodysuit may be enough on a tropical night. Keep checking the neck.
Do I really only need one sleeping bag, then?
For temperature regulation: yes. In practice, many parents still choose two—one in the wash and one in bed. But that is for practical reasons, not because the season requires it.
What should my baby wear under a merino wool sleeping bag?
In a room around 18–20 °C, a long-sleeved bodysuit is usually enough. If it is warmer, choose a short-sleeved bodysuit. Above 25 °C, often just a nappy. See our layering guide for an overview by temperature.
At what age can a baby sleep in a sleeping bag?
From birth, provided the size is correct: the neck opening must be narrow enough to prevent your baby from slipping inside, and the armholes must not be too loose. Never choose a sleeping bag for your baby to grow into. For all questions about safe sleep, always follow the current guidance from your child health clinic.