Best Sleep Sacks for Babies

By Angelica Videla — Certified Baby and Toddler Sleep Consultant, London | Supporting families across the UK, Europe, US, and Australia

Why sleep sacks matter for baby sleep

Sleep sacks serve two critical functions. First, they replace loose blankets in the cot, which is important for safe sleep. The Lullaby Trust and every major safe sleep organisation recommends against loose bedding for babies under 12 months. Second, and equally important for sleep quality, they help regulate temperature throughout the night.

Temperature regulation is one of the most underestimated factors in baby sleep. A baby who is too warm wakes more frequently. A baby who is too cold wakes earlier in the morning. A well-chosen sleep sack at the right TOG for the room temperature eliminates one of the most common causes of unnecessary night waking.

For detailed temperature guidance, see our complete guide: how to dress a baby for sleep by room temperature.

What to look for in a baby sleep sack

TOG rating. This measures thermal resistance — how warm the sleep sack keeps your baby. 0.5 TOG for summer, 1.0 TOG for spring and autumn, 2.5 TOG for winter. Some brands offer 3.5 TOG for very cold rooms.

Fit around the neck and arms. A sleep sack should be snug enough around the neckline that your baby cannot slip down inside it, but not so tight that it restricts breathing. Armholes should allow free movement without being loose enough to let cold air in.

Fabric quality. Organic cotton, bamboo, and merino wool are the most breathable options. Avoid polyester-heavy sacks which trap heat and increase the risk of overheating.

Ease of nappy changes. A two-way zip that opens from the bottom makes nighttime nappy changes significantly easier — and faster changes mean less disruption to sleep.

Room for growth. Most quality sleep sacks come in age-based sizes. Buying too large to get more use leads to a poor fit that compromises both safety and warmth.

Best sleep sacks by age

Newborn to 3 months

Ergopouch Cocoon Swaddle Bag. This is the sleep sack I recommend most often to newborn families. It combines a swaddle and sleep sack in one, with a zip-off swaddle wing that allows you to transition to arms-free when your baby starts rolling. The bamboo fabric is exceptionally soft and breathable.

Love to Dream Swaddle Up. For babies who prefer their arms up rather than swaddled down, this is the best option. The unique arms-up design accommodates babies who self-soothe by touching their face. Available in multiple TOGs.

3 to 12 months

Tommee Tippee Grobag. The most widely available and consistently reliable option in the UK. Available in 0.2, 1.0, and 2.5 TOG with clear temperature guides. The zip runs from top to bottom for easy nappy access. Good sizing and a wide range of designs.

HALO SleepSack. Simple, well-made, and available in cotton and fleece. The inverted zip opens from the bottom. A solid, no-fuss option that works well for families who want reliability without premium pricing.

Woolino 4-Season. Merino wool naturally regulates temperature, which means this sack works across a wider range of room temperatures without needing to switch between TOG ratings. More expensive than cotton alternatives but genuinely useful for families in homes where room temperature varies significantly.

12 months to 3 years

Ergopouch Sleep Suit Bag. Converts from a sleep sack to a wearable suit with legs, which is useful for toddlers who want to walk to bed. Available in 1.0 and 2.5 TOG.

Tommee Tippee Steppee. A sleep sack with feet holes that allow walking while still providing warmth and comfort. Works well for the transition period between cot and toddler bed.

Common mistakes with sleep sacks

• Using the wrong TOG for the room temperature — the most common cause of sleep sack-related night waking
• Buying a size too large for longer use — this compromises fit and safety
• Adding blankets on top of a sleep sack — this defeats the purpose and creates overheating risk
• Using a fleece sleep sack in a warm room — fleece does not breathe well and is best reserved for rooms consistently below 18 degrees
• Not checking the neckline fit — you should be able to fit two fingers between the neck opening and your baby’s neck

How the right sleep sack connects to better sleep

In my experience working with families, switching to the correct TOG sleep sack for the room temperature reduces unnecessary night waking in roughly 30 to 40 percent of cases where temperature was a contributing factor. It is one of the simplest, most cost-effective changes a family can make.

If your baby is waking frequently at night despite a good sleep environment, the issue may be schedule or settling-related. See our guides on night wakings and wake windows by age.