what TOG sleeping bag should I use for my baby?

Match TOG to room temperature: 2.5 TOG for 16-20 degrees, 1.0 TOG for 20-24 degrees, 0.5 TOG (or none) above 24 degrees, and 3.5 TOG below 16 degrees. The TOG must account for what baby is wearing underneath — a 2.5 TOG bag over a sleepsuit in a 20-degree room may be too warm.

can overheating cause SIDS?

Yes — overheating is an established independent risk factor for SIDS. A 1996 case-control study (Fleming et al., BMJ) found an adjusted odds ratio of 4.51 for SIDS in overheated environments after controlling for other risk factors. The leading hypothesis is that overheating impairs the arousal response that allows infants to rouse from dangerous situations during sleep.

what should my baby wear to sleep in a 20 degree room?

In a 20-degree room with a 2.5 TOG sleeping bag, a short-sleeve vest or light sleepsuit is appropriate. In a 2.5 TOG bag at 18-20 degrees, dress baby in a short-sleeve vest only. Use the back of the neck as a temperature check — warm but not sweaty is the target.

Room Temperature and SIDS: What the Numbers Say

Q: what temperature should a baby's room be at night?

16-20 degrees Celsius (60-68 Fahrenheit), per NHS, AAP, and Lullaby Trust guidelines. A room that feels slightly cool to an adult is appropriate for a sleeping infant. Above 20 degrees combined with heavy bedding significantly increases SIDS risk, per Blair 2006.

Q: how do I know if my baby is too hot at night?

Check the back of the neck or the chest — these should feel warm but not sweaty. Do not check the hands or feet, which are naturally cooler and not a reliable indicator of core temperature. Overheating signs include sweating, flushed skin, rapid breathing, restlessness, or damp hair.

Most SIDS prevention advice focuses on sleep position and environment (back to sleep, firm mattress, no loose bedding). Temperature gets less attention — but the evidence is clear: overheating is an independent risk factor for SIDS, and it’s one of the more controllable ones.

This is what the numbers say.

The Optimal Range

Most major health guidelines (NHS, AAP, Lullaby Trust) recommend a room temperature of 16–20°C (60–68°F) for infant sleep. Some guidelines extend this to 20°C as the upper limit; a few allow up to 22°C in specific circumstances.

The principle: a room that feels slightly cool to an adult is appropriate for a sleeping infant.

Why Temperature Matters for SIDS

The Overheating Mechanism

The leading hypothesis links overheating to impaired arousal. During deep sleep, the normal response to a threat (like reduced oxygen) is arousal — waking up. Overheating may blunt this arousal response, making it harder for an infant to rouse from a dangerous situation.

Overheating is also associated with increased viral illness severity and may compound other SIDS risk factors.

Fleming 1996 (BMJ)

Fleming et al. published a significant case-control study in the British Medical Journal examining thermal environment and SIDS risk. Key finding:

Overheating (high-tog bedding combined with room heating) had an adjusted odds ratio of 4.51 for SIDS — meaning infants in overheated environments were more than 4.5 times more likely to die of SIDS compared to those in cooler, lighter-bedding conditions.

This was after controlling for other known risk factors, meaning the temperature effect was independent, not just a proxy for something else.

Blair 2006

Blair et al. (follow-up CESDI/SUDI research) found that the highest SIDS risk occurred when room temperature exceeded 20°C combined with heavy bedding. The interaction between environmental heat and additional heat from bedding appeared particularly dangerous — each factor compounded the other.

This is why the recommendations aren’t just about room temperature in isolation. It’s the total thermal load on the baby.

The Thermoregulation Gap

Newborns cannot regulate their own body temperature effectively. Unlike adults, who sweat, vasodilate, and shiver to maintain core temperature, newborns:

Have a high surface area-to-volume ratio (lose heat faster)
Have limited ability to sweat (underdeveloped eccrine glands)
Cannot shiver effectively until several months old
Cannot remove covers or adjust their environment

This thermoregulatory immaturity persists until approximately 10–11 weeks of age, making early infants especially vulnerable to both heat and cold. During this window, the room environment and clothing choices matter more than at any other time.

TOG Ratings Explained

TOG (Thermal Overall Grade) measures the thermal insulation of a sleeping bag or blanket. Higher TOG = warmer.

Common ratings:

0.5 TOG: Summer, warm rooms (24°C+)
1.0 TOG: Transitional, mild rooms (20–24°C)
2.5 TOG: Standard, cool rooms (16–20°C)
3.5 TOG: Winter, cold rooms (below 16°C) — rarely needed with adequate room heating

The critical rule: TOG rating must be matched to both room temperature and what baby is wearing underneath.

Clothing + TOG Guide

Use this as a starting reference. Every baby is slightly different — check for overheating signs (see below).

Room Temp	Sleeping Bag TOG	What to Dress Baby In
Below 16°C	3.5 TOG	Long-sleeve vest + sleepsuit (footed pyjamas)
16–18°C	2.5 TOG	Short-sleeve vest + sleepsuit
18–20°C	2.5 TOG	Short-sleeve vest only (or light sleepsuit)
20–22°C	1.0 TOG	Short-sleeve vest only
22–24°C	1.0 TOG	Short-sleeve vest or just a nappy
Above 24°C	0.5 TOG or none	Nappy only, or light short-sleeve vest

Important: If you’re using loose blankets instead of a sleeping bag (not recommended for under 12 months), they should only come up to armpit height and be tucked securely under the mattress. A blanket that migrates over the face is a serious hazard.

Checking for Overheating

Don’t check the hands or feet — these are naturally cooler and not a reliable indicator of core temperature.

Check the back of the neck or the chest/tummy. These should feel:

Warm but not sweaty = appropriate
Hot or sweaty = too warm, remove a layer
Cold = too cold, add a layer

Other overheating signs:

Flushed or red complexion
Rapid breathing
Restlessness or unusual fussiness during sleep
Damp hair (sweating)

Thermometer Placement

A room thermometer is one of the most useful and underrated pieces of baby kit. To get an accurate reading:

Place it at baby’s level — not high on a wall (heat rises; ceiling temperature can be 2–3°C higher than floor level)
Keep it away from heat sources: radiators, heating vents, sunny windows
Away from cold drafts: outside walls, windows, air conditioning vents
Ideally in the middle of the room or near the crib

Check it before each sleep, not just at the start of the night — room temperatures fluctuate overnight as heating cycles on and off.

Practical Tips

In winter: Err on the side of cooler room + appropriate TOG rather than a warm room with lighter clothing. Consistent cool is easier to manage than fluctuating heat.

In summer: 24°C+ rooms are genuinely risky. A fan to circulate air (not blowing directly on baby) can help. Keep blinds closed during the day to reduce room temperature before the night feed.

Shared rooms: The AAP recommends room-sharing (but not bed-sharing) for at least the first 6 months. Be aware that two adults sleeping in a room raise the temperature — check the thermometer at the actual time you put baby down, not earlier.

Electric blankets / heated mattresses: Never. Baby cannot move away from a heat source. These are not safe for infant sleep.

The Simple Version

Room at 16–20°C. Match your TOG to the temperature. Check the back of the neck, not the hands. When in doubt, go cooler — a slightly cool room is safe; an overheated baby is not.

A room thermometer costs a few pounds. It’s probably the most impactful piece of equipment you own.