United States
Canada
Your Nursery Temperature Changed Before You Did
Somewhere around late April, the nursery starts doing something subtle but important: it warms up. Not dramatically — maybe two or three degrees overnight — but enough that the 2.5 TOG sleep sack your baby wore through February starts to feel like overkill. Most parents don’t notice until they check on their baby at midnight and find a flushed little face or a sweaty neck.
That’s the real signal to transition your baby’s TOG rating — not the date on the calendar, but the temperature in the room.
TOG stands for Thermal Overall Grade, a standardized measurement of how much thermal insulation a garment provides. A higher TOG rating indicates more thermal insulation and is suitable for colder temperatures, while a lower TOG rating is appropriate for warmer temperatures. In practical terms: your winter 2.5 TOG traps heat efficiently; your summer 0.5 TOG lets it escape. The number isn’t about how thick the fabric feels — it measures how warm a sleep sack is, not how thick or heavy it feels. A thin bamboo-muslin sack can be perfectly calibrated for a warm room in ways that a chunky fleece one simply isn’t.
The spring-to-summer transition is the trickiest time of year to get this right, because room temperatures don’t shift cleanly. A night in early May might hit 68°F in the nursery; by mid-June, that same room could be 76°F without air conditioning running. Managing that range — rather than picking one sack and hoping for the best — is what this guide is about.
The Temperature Numbers That Actually Matter
The most common mistake parents make is dressing baby for the weather outside rather than the temperature inside. The temperatures you should reference are those in your baby’s room, not the weather outside. A hot day doesn’t automatically mean a hot nursery if you have central air. A mild spring evening can still leave an upstairs room warm if heat rises through the house.
Get a simple room thermometer for the nursery — it takes the guesswork out entirely. Once you know the actual temperature, the TOG decision becomes much more straightforward:
- 75°F and above (24°C+): A 0.5 TOG sleep sack is the right call. At 75°F or higher, a TOG value of 0.5 to 1.0 is appropriate — a light layer of insulation that keeps baby comfortable without overheating. Pair with a short-sleeve bodysuit or, in rooms above 78°F, just a diaper underneath.
- 69–74°F (21–23°C): A 1.0 TOG tends to work well here, paired with a lightweight onesie. This is the range many US nurseries sit in during late spring with air conditioning.
- 64–68°F (18–20°C): A 2.5 TOG is still appropriate for this range, paired with warmer base layers.
The spring-to-summer transition typically means moving from 1.0 TOG to 0.5 TOG as your room consistently crosses 74°F at night. That crossover point is your trigger.
One nuance worth noting: if your home’s climate control keeps the nursery at a consistent temperature year-round, you may not need to switch at all — a 1.0 TOG can work year-round in a well-regulated room. But if your indoor temperatures shift with the seasons — which is the case in most US homes — choose a 0.5 TOG sleep sack for summer to ensure baby remains safe and comfortable.
How to Tell If Your Baby Is Already Too Warm
Babies can’t tell you they’re overheating, which is part of what makes this so stressful. Babies can’t regulate their own body temperature the way adults can — they rely entirely on the sleep environment and what they’re wearing to stay in their comfort zone. And the stakes matter: overheating in babies can raise the risk of sudden infant death syndrome (SIDS).
The check parents often reach for first — touching the hands or feet — is actually misleading. A baby’s circulation is still developing, so cool hands don’t mean a cold baby; check their chest or back instead. A chest or back that feels warm and dry is the sign you want. Sweaty, clammy, or flushed skin means it’s time to remove a layer or switch to a lower TOG.
Other signals your baby may be too warm at night:
- Waking more frequently than usual without obvious cause
- Flushed face or ears when you check on them
- Damp hair or neck at pickup
- Restless, unsettled sleep that isn’t explained by a developmental leap
And on the flip side, signs your child might be too cold include shivering, cold hands or feet, and fussiness — though in late spring and summer, overcooling is less common than overheating in most US homes.
If your baby looks flushed or feels sweaty, remove a layer immediately, even if the chart says they should be warm. The chart is a starting point. Your baby’s body is the final word.
Making the Switch: Practical Steps for the Transition Period
Spring doesn’t hand you a clean cutover date. For several weeks, you’ll probably have nights where the nursery is 70°F and nights where it’s 76°F. Rather than buying a new sack every time the temperature shifts five degrees, there’s a smarter approach: adjust the base layer underneath before you change the TOG.
You can extend the use of a 1.0 TOG sleep sack by changing the pajamas underneath — if the room is 74°F, use short sleeves; if it drops to 69°F, use a long-sleeved footed sleeper. Think of it this way: adding a thin cotton bodysuit is roughly equivalent to adding 0.5 to the insulation level. That gives you meaningful flexibility without needing a different sack every week.
A practical spring-to-summer transition plan:
Weeks 1–2 (nursery averaging 68–72°F): Stay in your 1.0 TOG. Swap footed pajamas for a lightweight long-sleeve onesie underneath.
Weeks 3–4 (nursery averaging 72–75°F): Move to your 0.5 TOG with a short-sleeve bodysuit. Check your baby’s chest temperature at the first nighttime feed.
Full summer (nursery consistently above 75°F): Commit to the 0.5 TOG. In rooms above 78°F, a diaper-only base layer is appropriate.
Also worth remembering: daytime nap temperatures and nighttime temperatures can differ enough to warrant different TOG choices. A nursery that sits at 73°F at 8pm might be 78°F during a 1pm nap. Checking the room temperature before each sleep — not just before bed — is the habit that makes the biggest difference.
For families with variable indoor temperatures, having a small collection of sleep sacks with varying TOG ratings ensures adaptability as weather fluctuates. You don’t need ten options — a 0.5 TOG and a 1.0 TOG covers the entire spring-to-summer range for most US homes.
What to Look for in a Summer Sleep Sack
Not all 0.5 TOG sleep sacks perform the same way. The TOG number tells you the insulation level, but the fabric determines how well the sack manages heat and moisture on a warm night.
Thickness doesn’t always tell you how warm a garment is — the type of material is often more important than the weight. Synthetic fabrics can be rated low-TOG but still trap heat and moisture in ways that natural fibers don’t. For summer, look for:
- Muslin or bamboo-blend fabrics — naturally breathable and moisture-wicking
- Sleeveless design — allows heat to escape from the arms and shoulders, where babies lose the most body heat
- 2-way zipper — makes nighttime diaper changes faster and less disruptive
- OEKO-TEX or similar certifications — confirms the fabric is free from harmful chemicals, which matters especially for babies with sensitive or eczema-prone skin
Loulou Lollipop’s 0.5 TOG Muslin Sleep Bag is built specifically for warm-weather sleep. It’s made from Tanboocel — a bamboo-cotton muslin blend — manufactured through a process that uses 99% less water than conventional cotton, making it both breathable and environmentally considered. The sleeveless, hip-healthy design supports free movement, and the sack is best suited for room temperatures of 75–81°F (24–27°C) — right in the range where most US nurseries land in summer. It was also named a Good Housekeeping 2025 Parenting Award winner, which reflects the kind of real-world testing parents can trust.
For the transitional weeks when your nursery sits between 68°F and 74°F, the 1.0 TOG TENCEL™ Lyocell Sleep Bag fills the gap — soft, breathable, and temperature-regulating without the weight of a winter sack.
The spring-to-summer switch doesn’t have to be complicated. Check the room, feel the chest, adjust the layer. Get those two pieces right, and the TOG number takes care of the rest.