Baby Sleep Sack Buying Guide (2027)

TOG measures how much warmth a fabric layer traps. As a rough guide, 0.5 suits rooms around 24 to 27 degrees, 1.0 suits rooms around 21 to 24 degrees, 2.5 suits rooms around 16 to 20 degrees, and pyjama weight shifts the result by roughly one step. Merino bags like Woolino's sit outside the scale because the fibre regulates temperature rather than trapping a fixed amount of heat. The practical method is a room thermometer, a known TOG, and a chest check: a sweaty chest means too warm, a cool chest means add a layer. Never buy by season name alone, because makers use summer, winter and all season to mean different things.

Age labels on sleep sacks vary between brands by months for the same baby, because babies vary by kilograms at birth and by centimetres at every check. Weight range first, length second, neck fit always: the neck opening must be too small for the head to slip through, and legs must kick freely without the bag riding up over the face. Universal snap bags like Woolino's solve the ladder by adjusting at the underarm, while sized bags demand a new purchase at each bracket. When between sizes, choose the larger size only if the neck still fits snugly.

Cotton is the washable workhorse: easy, durable, and the easiest fabric to live with daily. Bamboo rayon is silkier and suits sensitive skin, but wants gentler washing to keep its feel. Merino regulates temperature across seasons and justifies premium pricing for parents whose rooms swing. Muslin breathes in heat and gives almost no winter warmth, making it a summer specialist. Plush warms cold rooms and overheats warm ones, making it a winter specialist. Match fabric to room, skin and washing routine, in that order, and no fabric wins in general.

A sleep sack is used half asleep in the dark, so zip design matters more than print. Two-way zips that open from the bottom let parents change a nappy without stripping the baby, and zipper guards stop cold metal waking the child. Walker bags with leg openings and footed bags with feet exist for toddlers who stand, and they beat closed bottom bags for safety once climbing starts. Before buying, imagine the worst night change with that bag: if it needs a full strip, a torch and two hands, it will fail the 3am test no matter how good it looks folded.