How to Choose a Baby Sleep Sack: TOG and Warmth Explained
Some nights feel perfect: bath done, lullaby sung, baby drifting off like something out of a movie. Then there are the other nights, the ones where you keep wondering if baby is too warm, if the blanket is still in place, if you should add another layer. A baby sleep sack answers many of those questions at once. With winter around the corner, getting the warmth level right matters more than ever, so let's walk through how to pick one.
Article Summary
A sleep sack is a wearable blanket that stays put all night, so the main thing to choose is its warmth. This article explains how to read the TOG rating, match it to your baby's room temperature, and pick the right size and fit, fabric and zipper. It also covers winter layering, what baby can wear underneath, and the questions parents ask most often.
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Why Choose a Sleep Sack Over a Blanket?
We all love a soft blanket. But let's be honest: baby kicks it off in about thirty seconds flat. A sleep sack works like a wearable sleeping bag. It wraps around baby's torso and legs, leaves the arms free, and stays in place from bedtime to morning.
The Public Health Agency of Canada also points out that families who use a sleep sack don't need a blanket on top, and that the sack should suit the temperature of the room. The result: baby stays warm and cozy, and you stop playing the midnight game of "where did the blanket go?"
What to Look For in a Baby Sleep Sack
1. What Is TOG? A Sleep Sack TOG Chart
TOG is the unit used to measure how warm a sleep sack is. The higher the number, the warmer the sack. Here is a sleep sack TOG chart:
| TOG | Room temperature | Best for |
|---|---|---|
| 0.5 | Above 24°C (75°F) | Warm summer nights or heated rooms |
| 1 | 20 to 24°C (68 to 75°F) | A comfortable room temperature |
| 2.5 | 16 to 20°C (61 to 68°F) | Cool or cold nights |
| 3.5 | Below 16°C (61°F) | The chilliest bedrooms |
Brands rate TOG a little differently, so the label on your sleep sack always has the last word. Our product pages don't list a TOG, so for our sleep sacks, think of plush as the warmer option and organic cotton as the lighter one, then fine-tune with the layers underneath.
The best guide is the thermometer, not the calendar. If the room feels comfortable to you in light clothing, it will usually feel right for baby too. Many guides land between 20 and 22°C (68 to 72°F). A small thermometer on the dresser takes the guesswork out of bedtime.
2. The Size: How a Sleep Sack Should Fit
Size is all about fit and comfort. A sack that is too big bunches up around baby, and one that is too small gets in the way of kicking legs. Pick the size that matches baby's weight and length, following the manufacturer's size chart. Our sleep sacks come in three sizes, from 0/6 months up to 18/36 months.
Two fit rules are worth knowing:
- The neck and armholes should be snug enough that baby can't slip down inside the sack. Health Canada has recalled sleep sacks whose neck opening was too large, because an infant could slide inside.
- Skip weighted sleep sacks. The American Academy of Pediatrics advises against them for babies.
3. The Fabric: Soft and Breathable First
For nighttime, soft and breathable fabrics are the way to go. Organic cotton is a top choice: it feels gentle against a newborn's sensitive skin and holds up well through all those washes (because there will be many). For cooler rooms, our plush sleep sacks pair an ultra-soft plush polyester exterior with a breathable cotton lining.
4. The Zipper: Handy at 3 AM
A full-length zipper, like the one on our sleep sacks, makes quick diaper changes easy, so baby is more likely to drift right back to sleep. Shoulder snaps, which you'll find on our organic cotton sleep sacks, make getting baby in and out even easier.
How to Choose a Winter Sleep Sack
Winter makes everyone want to bundle up. But the temperature that counts is the one inside the bedroom, not the one outside.
Match the TOG to the Room, Not the Weather Outside
A well-heated home can be just as warm in January as in September, so check the thermometer at bedtime. If the room sits around 20 to 22°C (68 to 72°F), a 1 TOG sack is often enough, even during a cold snap. If the room drops below 20°C (68°F), say because of an older window or a cooler bedroom, a 2.5 TOG sack becomes useful. The 3.5 TOG ones are for the really chilly rooms.
Layer Underneath Before You Jump Up a TOG
The sleep sack is only one part of the warmth equation. A long-sleeve bodysuit, cotton pajamas and a sleep sack give you plenty of room to adjust. If baby feels a little cool, add a layer underneath. If baby feels warm, take one away. Our sleep sacks are sleeveless, so the long sleeves underneath take care of arms and hands.
Plush or Organic Cotton?
Both our plush and our organic cotton sleep sacks have a breathable cotton lining. The plush ones wrap baby in extra warmth for cooler nights, while the organic cotton ones suit milder rooms and the seasons in between. You'll find both in our sleep sacks for baby girls and sleep sacks for baby boys collections.
What Should Baby Wear Under a Sleep Sack?
A sleep sack doesn't replace clothing; it layers over it. The key is to match what baby wears underneath to how warm the sack is. As a general guide:
- With a light sleep sack (0.5 TOG): A short-sleeve bodysuit for baby girl or a light bodysuit for baby boy is all you need.
- With a mid-weight sleep sack (1 TOG): A lightweight cotton pajama set works great.
- With a warm sleep sack (2.5 TOG): Go for cozy pajamas for baby girl or a snug pajama set for baby boy, with a long-sleeve bodysuit underneath if the room is cold.
Looking for more soft layers? Our organic cotton collections for baby girl and baby boy are a good place to start.
A common check is to gently slip two fingers along the back of baby's neck. Warm and dry means just right. Damp means too hot. Cool means time to add a layer.
Our guide on how to dress baby for sleep also offers great seasonal tips and temperature references to help you dial things in.
When Can Babies Start and Stop Using a Sleep Sack?
Sleep sacks work from the earliest months, as long as you choose the right size. Our smallest size, 0/6 months, is made for the first months, and the largest, 18/36 months, takes you up to age three. Most babies can keep using one until age 2 or 3, depending on their size and stage of development.
One thing to keep in mind: some babies learn to pull themselves up to standing in their crib before they start walking. Once that happens, check that the sleep sack leaves enough room to move around comfortably.
The usual signs it's time to stop: baby starts climbing out of the crib, or you're moving to a toddler bed. Baby needs free legs to climb and walk, so switch to cozy pajamas at that point.
Common Questions Parents Ask
What Temperature Should Baby's Room Be?
A room between 20 and 22°C (68 to 72°F) suits most babies. The Public Health Agency of Canada's rule of thumb is simple: if the room feels comfortable to you, it will be comfortable for baby too. A small thermometer on the dresser makes it easy to check.
Can a Sleep Sack Be Used in a Car Seat?
A sleep sack is a bedtime layer, so it stays at home. For car rides, regular fitted clothing works better, with outerwear added according to the weather.
Should I Choose a Sleep Sack With Sleeves or Without?
It depends on the room temperature. Our sleep sacks are sleeveless, which makes them easy to adapt: a long-sleeve bodysuit or pajamas underneath covers cooler nights, while a short-sleeve bodysuit suits warmer rooms.
What TOG Do I Need for Winter?
Check the room temperature first, then use the chart above. A heated bedroom around 20 to 22°C (68 to 72°F) often calls for 1 TOG with warm layers underneath, while a room below 20°C (68°F) often calls for 2.5 TOG.
How Many Sleep Sacks Do I Need?
Ideally two: one in the wash, one in use. Any parent who has survived a night with a single soaked sleep sack will immediately understand why.
A Ritual That Helps Baby Settle
Beyond the practical side, the sleep sack often becomes an important signal for baby: it's part of the bedtime routine. Just like the song, the feeding, or the nightlight, zipping up the sleep sack becomes a cue that says, it's time to sleep now. And that kind of consistency makes bedtime easier for the whole family.