Sleep Sack Safety Guide: Choosing the Right Size and Thermal Rating

Feb 20, 2025

Ensuring your baby’s sleep environment is both safe and comfortable is a priority for every parent. Sleep sacks, also known as wearable blankets, offer a convenient and safe solution for keeping your baby warm without the risks of loose bedding.

The Sleep Syndicate will explore the safety considerations, proper sizing, and understanding the thermal ratings of sleep sacks to help you choose the best option for your baby. In addition, we will also look at how parents can improve their own sleep while caring for little ones with an online sleep habits improvement program

Understanding Sleep Sacks

Sleep sacks are designed to provide warmth while ensuring your baby remains comfortable and safe during sleep. They eliminate the need for loose blankets, which are associated with increased risks of suffocation and Sudden Infant Death Syndrome (SIDS) [1]. By allowing babies to move freely, sleep sacks support safe sleep practices and are recommended by the American Academy of Pediatrics (AAP) as a safer alternative to blankets for infants under 12 months old [2].

Safety Considerations

When selecting a sleep sack, ensure the following safety guidelines are followed:

Proper Fit

A key safety consideration is the proper fit of the sleep sack. It should be snug around the neck and armholes, but not so tight that it restricts movement or causes discomfort. An ill-fitting sleep sack can pose strangulation hazards or increase the risk of overheating. Furthermore, a loose or overly large sleep sack may accidentally ride over your baby’s face during sleep, posing a suffocation risk [3].

TOG Rating and Temperature Control

TOG (Thermal Overall Grade) ratings indicate the warmth of a sleep sack. An essential factor in preventing overheating or chilling is ensuring the sleep sack matches the ambient room temperature. Overheating has been linked to an increased risk of SIDS [4], making it critical to select a sleep sack with the appropriate TOG rating for the season and your baby’s comfort.

Material Choice

Selecting breathable materials is also vital in preventing overheating. Organic cotton, muslin, and bamboo are popular fabric choices for sleep sacks. These materials are breathable and help regulate your baby's body temperature. Avoid synthetic fabrics that may trap heat and moisture, contributing to an uncomfortable and unsafe sleep environment [5].

Transitioning from Swaddling

For newborns, swaddling offers comfort and a sense of security by mimicking the tight environment of the womb. However, once your baby begins to show signs of rolling over, it's a good time to transition to a sleep sack if desired. Introducing a sleep sack that allows for free arm movement will provide both comfort and safety [6].

Sizing Guide

Choosing the right size sleep sack ensures your baby can move freely while remaining safe and secure. Here’s a general guideline to help you choose the appropriate size based on your baby’s weight and height:

Newborn (0-3 months): Suitable for babies weighing up to 12 pounds (5.4 kg).
Small (3-6 months): For babies weighing 12-18 pounds (5.4-8.2 kg).
Medium (6-12 months): Fits babies weighing 16-24 pounds (7.3-10.9 kg).
Large (12-18 months): Designed for babies weighing 22-28 pounds (10-12.7 kg).
Extra Large (18-24 months): For toddlers weighing 26-36 pounds (11.8-16.3 kg).

Make sure to refer to the manufacturer’s specific sizing chart, as sizes may vary slightly. Ensuring a correct fit allows for proper leg movement, contributing to your baby’s hip development and comfort [7].

Understanding TOG Ratings

TOG ratings help parents choose sleep sacks according to their baby’s needs for warmth in different environments. Here are the general guidelines for selecting the appropriate TOG rating based on room temperature:

0.5 TOG: For room temperatures above 75°F (24°C). Ideal for warmer climates and summer months.
1.0 TOG: Best for room temperatures between 69-74°F (21-23°C).
2.5 TOG: For cooler room temperatures between 61-68°F (16-20°C). Suitable for fall and winter.
3.5 TOG: For temperatures below 61°F (16°C), typically used in cold climates or winter months.

Ensure your baby is dressed appropriately underneath the sleep sack to prevent overheating or discomfort. Babies dressed too warmly may be at a higher risk for heat stress or SIDS, which is why careful temperature regulation is crucial [8].

Transitioning to a Sleep Sack

As your baby reaches the developmental stage where they begin to roll over, you may want to consider transitioning from a swaddle to a sleep sack. If you do decide to use a sleep sack for your child, a gradual transition can help make the change less disruptive for both the baby and the parent. Here's a step-by-step approach:

Introduce During Naptime: Start by using the sleep sack during daytime naps. This allows your baby to adjust without the pressure of a full night’s sleep.
One Arm Out: If your baby is used to being swaddled, leave one arm out of the swaddle for a few nights, allowing them to get used to the feeling of a loose arm.
Full Transition: After your baby becomes comfortable with one arm out, switch entirely to a sleep sack, ensuring both arms are free to move.

This gradual approach supports your baby’s development and helps minimize sleep disruptions during the transition [9].

Seasonal Considerations

The seasons play a significant role in selecting the appropriate sleep sack. Room temperatures change throughout the year, so it’s essential to choose the right TOG rating based on seasonal variations:

Spring/Summer: Opt for sleep sacks with lower TOG ratings (0.5-1.0). These are typically made from breathable materials such as cotton or muslin.
Fall/Winter: Choose sleep sacks with higher TOG ratings (2.5-3.5) for warmth. Layer your baby’s clothing accordingly, but be cautious not to overdress, as it may lead to overheating.

Monitor your baby’s temperature by checking their neck or back to ensure they are not too hot or too cold. A baby’s body temperature can fluctuate rapidly, so regular adjustments to their sleep attire may be necessary [10].

For The Parents

Sleep sacks are a safe, convenient, and comfortable solution for keeping your baby warm during sleep. By understanding proper fit, selecting the right size, and choosing the appropriate TOG rating, parents can help ensure their baby gets a safe, restful night’s sleep. As your baby transitions from swaddling to a sleep sack, following a gradual approach can help maintain comfort while reducing potential safety risks. Finally, by considering seasonal changes and adjusting your baby’s sleep attire accordingly, you can optimize their sleep environment year-round.

For parents looking for help to improve their own sleep habits while caring for a baby, The Sleep Syndicate can be an invaluable resource, offering a sleep habits improvement program, personalized nudges, educational content, and nightly wind-down routines that will maximize a parent’s chances of getting that much needed, quality sleep.

Take Care Of Your Sleep With The Sleep Syndicate

Citations

De-Kun Li, Diana B. Petitti, Marian Willinger, Robin McMahon, Roxana Odouli, Hong Vu, Howard J. Hoffman, Infant Sleeping Position and the Risk of Sudden Infant Death Syndrome in California, 1997–2000, American Journal of Epidemiology, Volume 157, Issue 5, 1 March 2003, Pages 446–455, https://doi.org/10.1093/aje/kwf226
Glover Williams, A., & Finlay, F. (2019). Can infant sleeping bags be recommended by medical professionals as protection against sudden infant death syndrome?. Archives of disease in childhood, 104(3), 305–307. https://doi.org/10.1136/archdischild-2018-316093
Faurie, C. (2023). Increased temperatures and child health outcomes: a systematic review. European Journal of Public Health. 33. 10.1093/eurpub/ckad160.1161.
Jingxian Xu, Yehu Lu, Lanjun Yin, Haibo Song. Investigation on the preferred thermal properties of sleeping bag and indoor environment for preschool-aged children: Towards sleeping thermal comfort, Case Studies in Thermal Engineering. Volume 52, 2023, 103701. ISSN 2214-157X. https://doi.org/10.1016/j.csite.2023.103701. https://www.sciencedirect.com/science/article/pii/S2214157X23010079)
Van Sleuwen, B. E., Engelberts, A. C., Boere-Boonekamp, M. M., Kuis, W., Schulpen, T. W. J., & L’Hoir, M. P. (2007). Swaddling: A Systematic Review. PEDIATRICS, 120(4), e1097–e1106. doi:10.1542/peds.2006-2083
Salm Ward, T.C., Balfour, G.M. Infant Safe Sleep Interventions, 1990–2015: A Review. J Community Health 41, 180–196 (2016). https://doi.org/10.1007/s10900-015-0060-y
Bach, V., & Libert, J. P. (2022). Hyperthermia and Heat Stress as Risk Factors for Sudden Infant Death Syndrome: A Narrative Review. Frontiers in pediatrics, 10, 816136. https://doi.org/10.3389/fped.2022.816136
Dixley, A., & Ball, H. L. (2022). The effect of swaddling on infant sleep and arousal: A systematic review and narrative synthesis. Frontiers in pediatrics, 10, 1000180. https://doi.org/10.3389/fped.2022.1000180
Cohen, D., Atun-Einy, O., & Scher, A. (2012). Seasonal effect on infants' sleep regulation: a preliminary study in a Mediterranean climate. Chronobiology international, 29(10), 1352–1357. https://doi.org/10.3109/07420528.2012.728654

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