TOG 3.5 vs. TOG 2.5 Sleep Sack: Which Does a Canadian Baby Need in Winter?

The Question Most Parents Get Backwards

Most Canadian parents shopping for a winter sleep sack assume the answer is simple: colder country, warmer sack. Buy the highest TOG available and call it done. But that logic skips the one variable that actually determines which rating your baby needs — and it has nothing to do with what’s happening outside.

The outdoor temperature is almost irrelevant once your furnace is running. What actually determines which TOG rating your baby needs is the temperature inside the nursery at night. That shift in framing changes the whole decision.

TOG stands for Thermal Overall Grade — a standardized unit of measurement used to describe how effectively a garment traps warm air close to the body. The TOG rating of baby sleepwear is determined through standardized testing using a thermal mannequin, and takes into account factors such as the type of fabric, the thickness of the material, and the construction of the garment. A higher number means more insulation — but more insulation is only the right call when the room actually requires it.

Babies can’t regulate their own body temperature the way adults can, especially in the first 12 months. If they’re dressed too warmly, they’re at higher risk of overheating, which is a known risk factor for SIDS. So the goal isn’t the warmest possible sack — it’s the right one for your specific nursery.

What TOG 2.5 and TOG 3.5 Actually Cover

Both ratings sit at the warmer end of the sleep sack spectrum, but they’re designed for different conditions.

TOG 2.5 is the standard winter sleep sack for most families. A 2.5 TOG sleep sack is designed for rooms between 16–20°C (61–68°F). In a Canadian winter context, that typically means older homes with poor insulation or drafty windows, nurseries on exterior walls that get less heat from the central system, and households that lower the thermostat significantly at night.

TOG 3.5 occupies a narrower use case. It’s designed for very chilly nights where room temperatures drop below 16°C. You’d reach for a 3.5 TOG when the room temperature sits between 14–16°C (57–61°F). That’s cold enough that most Canadian homes with functioning central heating rarely get there.

Here’s a quick comparison:

Unless your home genuinely drops below 16°C overnight, you probably don’t need TOG 3.5 in Canada. It’s a rating built for environments that most heated Canadian homes don’t reach.

How Canadian Homes Actually Behave in Winter

When outdoor temperatures drop to -20°C in January and your furnace is running on a schedule, the nursery temperature can shift by four or five degrees between midnight and 5am — especially in older homes with drafty windows or inconsistent baseboard heating. That swing matters, but it rarely pushes a well-heated nursery below 16°C.

According to Canadian HVAC data, most households set thermostats to 20–22°C during the day, and some dial it back to 17–19°C at night to save on heating costs. A nursery landing at 17–19°C overnight is exactly the sweet spot where TOG 2.5 performs well. A nursery that stays at 20–22°C throughout the night probably only needs a TOG 1.0 with appropriate pajamas underneath.

Canadian homes vary more than the average TOG chart accounts for. A condo in Vancouver with radiant floor heating holds temperature differently than a 1970s bungalow in Winnipeg with baseboard heaters that cycle on and off through the night. So before buying anything, spend a week checking nursery temperature at the times your baby actually sleeps — particularly in the early morning hours when heating systems tend to cycle down.

And one thing that catches parents off guard: cold hands and feet are not a reliable indicator of an underdressed baby. Newborn circulation prioritizes the core, and extremities run cold as a default. A baby who runs warm — you’ll notice this by checking the back of the neck and the chest, neither of which should be sweaty — needs slightly less insulation than the chart suggests.

The Layering Variable Nobody Talks About Enough

TOG ratings don’t exist in isolation. The clothes worn underneath the sleep sack contribute meaningfully to total warmth, which means you can often achieve the right thermal environment with a lower-rated sack and smarter layering — rather than jumping straight to TOG 3.5.

Layering allows great flexibility in keeping babies warm and cozy without overheating, and each additional layer of clothing adds to the overall TOG rating.

A practical layering guide for Canadian nurseries:

• Room at 20–22°C: Light onesie + TOG 1.0 sleep sack
• Room at 17–20°C: Footed pajamas or long-sleeve onesie + TOG 2.5 sleep sack
• Room at 16–17°C: Footed pajamas + TOG 2.5 sleep sack (or add a bodysuit underneath)
• Room below 16°C: Long-sleeve onesie + footed pajamas + TOG 3.5 sleep sack

For most Canadian families, the jump from TOG 2.5 to TOG 3.5 is solved by adding a layer underneath the 2.5 before buying a new sack. A rule of thumb worth using: dress yourself for the room temperature, then add one layer for the baby. If you’re comfortable in a long-sleeved shirt at 20°C, your newborn probably wants that shirt equivalent plus the TOG 1.0 sleep sack.

And fabric matters here too. TENCEL Lyocell, the fabric used in many premium sleep sacks, is a naturally moisture-wicking, thermoregulating fiber. Babies dressed in TENCEL tend to stay more comfortable across a wider temperature range than they would in a heavier synthetic fill, because the fabric responds to body heat rather than just trapping it statically.

Which One Does a Canadian Baby Actually Need?

The honest answer: for the vast majority of Canadian families, TOG 2.5 is the right winter sleep sack. TOG 3.5 is a legitimate product, but it solves a problem most heated Canadian homes don’t have.

A TOG 2.5 for November through March covers the months when central heating gets its full workout. A TOG 1.0 for April through October, with some overlap in both directions depending on where in the country you live and how your home handles temperature. Families in BC’s Lower Mainland might lean on the TOG 1.0 almost year-round given milder winters. Families in Winnipeg or Regina probably want that TOG 2.5 from October.

Where TOG 3.5 does make sense:

• Homes where the nursery genuinely drops to 14–16°C overnight (older homes with minimal insulation, or rooms far from the furnace)
• Families who keep the house very cold at night for energy savings
• Situations where heating is unreliable — a power outage, a broken furnace, or a cold snap that outpaces the heating system

For everyone else, TOG 3.5 tends to run warm in a properly heated Canadian nursery and risks overheating a baby who already has footed pajamas on underneath.

Loulou Lollipop’s TENCEL Sleep Bag 2.5 TOG is built specifically for the Canadian winter context: made from TENCEL Lyocell, the 2.5 TOG sleep sack keeps the baby safe and warm all night. It features a 2-way zipper for easy diaper changes and is insulated with DuPont Sorona fill. The 1.0 TOG version covers the shoulder seasons and heated homes where the nursery stays above 20°C — made from TENCEL Lyocell and organic cotton, the 1.0 TOG all-season sleep sack keeps the baby cozy and comfortable all night, and can’t be kicked off. Both are manufactured at an OEKO-TEX Standard 100 certified factory, so you can feel confident the sleep bags are free of toxic chemicals.

The simplest approach for most Canadian families: own a TOG 1.0 and a TOG 2.5. Adjust the pajamas underneath based on the week’s forecast. Some families keep one of each on hand and switch based on the week’s forecast — a reasonable approach given how variable Canadian winter temperatures can be from November through March. TOG 3.5 is worth considering only if your nursery consistently reads below 16°C overnight — and if it does, that’s probably worth fixing at the heating level before solving it with a sleep sack.