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A 3.5 TOG sleep sack is made for rooms between 57–61°F (14–16°C) — typically an unheated bedroom in winter. Note that this band has a floor as well as a ceiling: below 57°F (14°C), the answer is a warmer room rather than a warmer sleep sack.
Health guidance puts the ideal nursery temperature at 16 to 20°C, so 3.5 TOG is for rooms that have dropped below that range and cannot easily be warmed. If you can raise the room into that range, a 2.5 TOG sack is the better match.
When the room's lowest overnight temperature falls below 61°F (16°C). Go by a thermometer reading taken in the coldest part of the night, not by the calendar — a room that reads 65°F at bedtime can easily be at 58°F by 5am, and that is the temperature your baby is sleeping in.
Above 61°F (16°C), 2.5 TOG is the right rating. See Ideal Room Temperature for Newborns.
Not in the room it is designed for — 57–61°F (14–16°C) — but it is too warm above 61°F (16°C). The temperature-sensing sticker on every Kaiya Baby sleep sack tells you at a glance: blue means a little cold, yellow means comfortable, orange or brown means too warm.
If you are unsure, choose the lower TOG and add a layer underneath rather than keeping a higher TOG in a warmer room — a layer is easy to remove at 3am, a sleep sack is not. The AAP advises against letting a baby get overheated during sleep; the signs to watch for are in Is My Baby Too Hot While Sleeping?
It comes down to how cold your room actually gets overnight. If it holds at 61–68°F (16–20°C), 2.5 TOG is the right rating. If it regularly drops to 57–61°F (14–16°C), 3.5 TOG is what that room needs.
A common mistake is to keep a 2.5 TOG sack in a colder room and pile on layers underneath. Bulky layers restrict movement and are harder to get right than simply matching the sack to the room. If your room sits below 57°F (14°C), warm the room first — no sleep sack should be asked to compensate for that.
One layer, adjusted within the band. Near 61°F (16°C), a long-sleeve bodysuit. Around 59°F (15°C), a long-sleeve bodysuit with footed pants. Near 57°F (14°C), add a light pyjama layer on top of that.
The fold-over cuffs can be pulled down over the hands on the coldest nights, which is usually enough without adding another layer. Never a hat indoors. Full guidance in What to Wear Under a Sleep Sack.
Yes, on both counts, as long as the room genuinely sits at 57–61°F (14–16°C) and the sack fits. Our 0–6 month size fits babies 21–27" (53–69 cm) and 7–18 lbs (3–8 kg); the neckline should sit close without riding up toward the chin.
3.5 TOG is designed for a full night in a cold room, which is exactly the situation where a wearable blanket is safer than loose bedding — nothing to kick off, nothing to cover the face. See the AAP's safe sleep guidance and our Safety & Certifications page.
Yes, for rooms down to 57°F (14°C). 3.5 TOG is our warmest rating and is built for exactly this — winter bedrooms without heating, or rooms that lose several degrees overnight.
If your room is colder than 57°F (14°C), the right move is to warm the room rather than to look for a higher TOG. Guidance from The Lullaby Trust puts the ideal range at 16–20°C, and no sleep sack is intended to make up the difference for a room well below it. Browse the full winter range.
No. A heated room usually sits at 68–75°F (20–24°C), which is 1.0 TOG territory. Putting a 3.5 TOG sack on a baby in a heated room is the most common way to overheat them.
Central heating often keeps a nursery above 68°F all night even in January, so check the thermometer rather than the weather outside. If heating runs only part of the night and the room drops afterwards, choose the TOG that matches the coldest reading — often 2.5 TOG.
Yes — every 3.5 TOG sleep sack has long sleeves with fold-over cuffs. There is no sleeveless 3.5 TOG, and no 3-in-1 at this rating: a room cold enough for 3.5 TOG needs covered arms.
That leaves two styles. Long Sleeve is for babies who sleep in the crib. Long Sleeve Walker is for babies who are standing, cruising or walking before bed and need free legs.
Machine wash at 40°C (104°F) with a mild detergent, zipper fastened, inside a laundry bag. No fabric softener, no bleach, no soaking. Tumble dry on low or line dry — do not dry clean.
Thicker sacks worry parents most on this point, but camel wool and SORONA® recover their loft in the dryer rather than matting down, so the sack keeps its shape and its warmth.
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