By the Babbez Editorial Team
What should your baby wear to sleep? For most nights, a light base layer under a correctly sized sleep sack — a wearable blanket that zips over pajamas and keeps your baby warm with nothing loose in the crib. The American Academy of Pediatrics (AAP) recommends a properly sized wearable blanket instead of loose blankets, and warns against overheating.
Key takeaways
- A sleep sack is the wearable-blanket alternative the AAP recommends in place of loose blankets.
- TOG is a textile warmth rating, not a safety standard; choose the TOG that matches your room temperature.
- Size by your baby current weight and height, not age; the AAP advises the sack be the correct size and not cover the face.
- Adjust warmth with the layer worn under the sack, and never stack two sacks.
- The AAP advises stopping swaddling as soon as your baby shows signs of trying to roll.
- The AAP and the U.S. CPSC advise against weighted sleep sacks, swaddles, and blankets.
This guide is general information from the Babbez Editorial Team, not medical advice. For safe-sleep decisions, follow the AAP and your pediatrician, and read our medical disclaimer.
What is a baby sleep sack?
A baby sleep sack is a wearable blanket: a sleeveless, zip-up pouch your baby wears over pajamas so they stay warm while the crib stays bare. The AAP describes a bare sleep surface — a firm, flat mattress with a fitted sheet and nothing else — as the safest setup, and names a correctly sized wearable blanket as the alternative to loose bedding. The arms stay free so your baby can move, and sizes run from newborn into toddlerhood.
Common features include a two-way zipper for nighttime diaper changes, a chin guard, a roomy leg area for the hips, and foot openings on toddler sizes. Classic sacks are sleeveless on purpose so bare arms can vent heat; for a cold room, keep the sleeveless sack and add a long-sleeve bodysuit underneath rather than thick attached sleeves that trap heat.
Newborn sleepwear and first sleep sacks live in our baby girl newborn and baby boy newborn collections, sized for the earliest weeks.
What does TOG mean on a sleep sack?
TOG stands for thermal overall grade, a textile measure of how warm a garment is: the lower the number the cooler and lighter the sack, the higher the number the more insulating it is. Baby sacks are commonly sold from about 0.2 to 0.5 TOG (lightest, for warm rooms) up to about 3.5 TOG (heavily padded, for cold rooms). Contrary to how it is sometimes marketed, TOG is a manufacturer rating, not an AAP or medical standard — it is simply a tool for matching a sack warmth to the room.
The table below is a general guide many manufacturers publish, shown here for illustration only, not as medical guidance. Follow the AAP and your pediatrician, and always check the chart for the specific sack you buy.
| TOG rating | Room temperature | What it suits |
|---|---|---|
| 0.2–1.0 TOG | 75°F and above (24°C+) | Warm room; lightest fabric, minimal underlayer |
| 1.0–2.5 TOG | 68–75°F (20–24°C) | Average room; light insulation over a light base layer |
| 2.5–3.5 TOG | 61–68°F (16–20°C) | Cooler room; more warmth over a long-sleeve base layer |
| 3.5 TOG and up | Below 61°F (16°C) | Cold room; higher insulation over warmer layers |
How do I choose the right TOG for the room temperature?
Start with the room, not the calendar: measure the nursery temperature, pick one sack TOG that matches it, then fine-tune with the layer underneath. We call this the Room-First Method — set the sack to the room, adjust with the base layer, and never combine two sacks. Many families keep the nursery around 68 to 72°F (20 to 22°C), a comfort preference, not a rule.
Because a too-warm baby cannot tell you, watch for the signs the AAP names: sweating, a hot chest, or flushed skin. A practical check is to feel the chest or back of the neck rather than the hands and feet, which normally run cooler. The AAP advises dressing a baby in only one more layer than an adult would wear in the same room, warns that overheating raises risk, and advises against a hat indoors once you are home from the hospital, because heads release heat. If you see those signs, remove a layer.
What size sleep sack does my baby need?
Size a sleep sack by your baby current weight and height rather than age; weight is the better guide, since bands overlap between brands and a sack that is too big can slide up toward the face. The AAP advises the wearable blanket be the correct size and not cover the head or face, so choose the size that fits now rather than sizing up, keeping the neck and armholes snug. A clear sign to size up: your baby feet nearly reach the bottom, or the chest and armholes feel tight.
The ranges below are illustrative bands from US brand charts (HALO, aden + anais, Nested Bean); they overlap, so confirm the chart for the sack you choose. Many US brands set a minimum weight of about 7 lb.
| Typical size label | Weight | Age (guide only) |
|---|---|---|
| Newborn / XS | 7–13 lb | 0–3 months |
| Small | 14–20 lb | 3–6 months |
| Medium | 18–30 lb | 6–18 months |
| Large / Toddler | 28–42 lb | 18–36 months |
What should my baby wear under a sleep sack?
The AAP guideline is one more layer than an adult would wear in the same room: think diaper and short-sleeve bodysuit in a warm room, a long-sleeve bodysuit or footed pajamas in a cool one. Adjust warmth here, not with a heavier sack.
As a starting point many manufacturers publish (a comfort guide, not a medical rule):
- 75°F and up (24°C+): a diaper or short-sleeve bodysuit under about a 0.5 TOG sack.
- 68–75°F (20–24°C): a short- or long-sleeve bodysuit under about a 1.0 TOG sack.
- 64–68°F (18–20°C): a long-sleeve bodysuit or footed pajamas under about a 2.5 TOG sack.
- Below 64°F (18°C): footed pajamas, and socks if needed, under about a 3.5 TOG sack.
Which sleep sack material is best: cotton, bamboo, merino, or fleece?
There is no single best material; it depends on your room, the season, and your baby skin. Cotton is breathable, easy to wash, low cost, and a reliable all-rounder, with organic versions a common pick for delicate skin.
Bamboo viscose is soft, wicks moisture, and regulates temperature well for warm rooms; it is a manufactured cellulose fiber, not raw bamboo. Merino wool is a standout natural regulator, warm in the cold and breathable in the warm, though it costs more. Fleece (polyester) is cozy for cold rooms but less breathable, and can run warmer than its stated TOG, so many families keep it to winter and watch for the overheating signs the AAP describes.
Sleep sack vs swaddle: which one and when?
A swaddle and a sleep sack solve different stages. A swaddle is a snug wrap that holds a newborn arms-in to calm the startle (Moro) reflex in the early weeks; a sleep sack is a wider zip pouch that leaves the arms free so an older baby can move and roll.
The practical switch is timing. The AAP advises stopping swaddling as soon as your baby shows any sign of trying to roll — as early as 2 months for some — and before your baby can roll independently. Because that day arrives without warning, many families move to an arms-free sleep sack proactively, using a transition swaddle that goes arms-in, then one arm out, then arms free.
How do I swaddle a newborn safely?
The AAP describes swaddling as a snug wrap that can soothe a newborn in the early weeks; done safely, it stays firm across the chest but loose around the hips, with the baby on their back. Here is the basic method.
- Spread a thin, square swaddle blanket in a diamond and fold the top corner down a few inches.
- Lay your baby face-up with the shoulders just below the folded edge.
- Straighten one arm along the body, bring that side of the blanket across the chest, and tuck it under the opposite side.
- Fold the bottom up, leaving room for the hips and knees to bend; the AAP advises leaving room for the baby hips to move.
- Bring the last corner across and tuck it in, keeping every layer clear of the neck and face.
- Check the fit the way the AAP describes: slip two or three fingers between your baby chest and the wrap.
Two rules carry the most weight: the AAP advises always placing a swaddled baby on their back to sleep, and stopping swaddling at the first sign of rolling, because the risk of suffocation is higher if a swaddled baby rolls onto the stomach.
Are weighted sleep sacks safe?
The AAP advises against weighted sleep sacks, weighted swaddles, and weighted blankets for babies, so Babbez does not recommend or sell them. The AAP explains that added weight can press on a baby chest and has been linked to lower oxygen levels. In 2024 the U.S. Consumer Product Safety Commission (CPSC) separately warned that weighted infant swaddles and blankets are unsafe for sleep and urged retailers to stop selling them.
Following those warnings, major retailers including Target, Walmart, Nordstrom, and Babylist committed to stop selling weighted infant products. If you are shopping for warmth, the AAP-aligned path is a correctly sized, unweighted sleep sack at the right TOG for your room.
When can my baby use a sleep sack, and when should swaddling stop?
A sleep sack can be used from the newborn stage through toddlerhood, in sizes that run to around 36 months, so most babies never age out of it. Swaddling is the opposite: the AAP advises stopping early, as soon as your baby shows any sign of trying to roll, which can begin around 2 months — watch your own baby development, not a fixed date. Most babies settle into an arms-free sack within about 3 to 7 nights, and an arms-out transition sack can smooth the change.
Sleep sack questions parents ask
Do newborns sleep better in a sleep sack or a swaddle
Both work; the choice is about your baby. A swaddle calms a newborn startle reflex in the first weeks, while a sleep sack keeps the arms free from day one. The AAP allows either when used correctly, on the back, and advises moving away from swaddling once your baby shows signs of trying to roll.
What TOG sleep sack is best for summer
For a warm summer nursery, a light sack in the 0.2 to 1.0 TOG range is the usual pick, often with just a diaper or a short-sleeve bodysuit underneath. Remember TOG is a manufacturer comfort rating, so check the room temperature and the AAP overheating signs rather than the season alone.
Can my baby wear a sleep sack with arms out
Yes. Arms-out is the standard design once a baby is past the swaddle stage. Free arms let your baby push up and move, which matters most once rolling begins; the AAP advises arms should be free by the time a baby can roll.
Should I buy a bigger sleep sack for room to grow
The AAP advises a wearable blanket be the correct size and not cover the face, so choose the size that fits now rather than sizing up. A sack that is too large can slide toward the head; one sized to current weight and height keeps the neck and armholes snug.
Sources: AAP (HealthyChildren.org): How to Keep Your Sleeping Baby Safe; AAP (HealthyChildren.org): Swaddling, Is It Safe for Your Baby; AAP Pediatrics: Sleep-Related Infant Deaths, Updated 2022 Recommendations; U.S. CPSC: Weighted Infant Swaddles and Blankets Are Unsafe for Sleep (2024); U.S. CPSC: Retailers Commit to Stop Selling Weighted Infant Products (2024). TOG and sizing ranges are illustrative manufacturer guides (HALO, aden + anais, Nested Bean, ergoPouch); always follow the chart for the product you buy. This article is general information, not medical advice; see our medical disclaimer.
