A wool blanket is one of the few pieces of warmth kit that needs no power, no fuel and no batteries, works even when it's slightly damp, and earns its keep on the sofa the other three hundred days of the year. In a UK winter power cut — the boiler off, the heating dead, the house slowly cooling — a good wool blanket over your knees or wrapped round a child is the calm, low-tech backstop that keeps you comfortable while you sort everything else out. The catch is that "wool blanket" covers everything from a genuine dense pure-wool army-surplus blanket to a thin acrylic throw with "wool" only in the marketing. This guide explains which is which, how warm a blanket actually is, and how it fits alongside the rest of your warmth kit.
If you're still deciding between a blanket and a sleeping bag for backup warmth, read sleeping bags vs blankets first — this guide assumes you want a blanket and focuses on choosing a good one.
Why wool, and not just any blanket
Wool has three properties that matter when the heating's off. It insulates even when damp — the fibres trap air and keep warming you where a wet cotton or acrylic blanket just goes cold and clammy, which is exactly why wool has been the traditional choice for camps, ambulances and mountain rescue. It's naturally flame-resistant — wool tends to smoulder and self-extinguish rather than melt and flare like acrylic, a real advantage if you're near candles, a stove or an open fire during an outage. And it's breathable, so you stay warm without the sweaty overheating you get under synthetics. A foil emergency blanket reflects your heat back brilliantly for its weight, but it's a single-use plastic sheet that rustles, tears and traps condensation; a wool blanket is the comfortable, durable, reusable version you'll actually want to sit under for hours.
Read the label: pure wool, lambswool, merino, blend or "wool-look"
The single most important thing on the label is the fibre content. "Pure new wool" or "100% wool" is the warmest and most flame-resistant — classic dense grey army-surplus and heritage blankets fall here, and they're heavy, hard-wearing and superb value. Lambswool, like the WoolStudio lambswool blanket in our picks, is softer and finer, warm and comfortable for indoor use and everyday bedding. Merino is the softest and least itchy, often used in lighter throws, and lovely against skin but usually thinner. A wool blend (say 70% wool / 30% synthetic) is a sensible middle ground — most of wool's warmth and flame behaviour at a lower price and weight. What to be wary of is a blanket described as "woollen-feel", "wool-effect" or with wool buried far down a mostly-acrylic ingredient list: that's a synthetic throw, and it will melt near flame and go cold when damp. If the brand won't state a clear percentage, assume it's mostly synthetic.
How warm is it? Weight and GSM
For a blanket, warmth tracks closely with how much wool is in it — so weight and GSM (grams per square metre) are your best guide. As a rough steer for a UK winter: a light throw around 300–400 GSM is a sofa layer, comforting but not enough on its own in a cold house; a mid-weight blanket of roughly 500–700 GSM is the sweet spot for power-cut warmth, genuinely toasty layered over clothes; and a heavy 700 GSM-plus pure-wool blanket (the army-surplus type, often 1.5–2 kg) is seriously warm and near-indestructible, at the cost of bulk. Bigger is warmer too — a blanket that fully wraps you and tucks under, rather than one that leaves your feet out, makes a real difference. If in doubt for emergency use, size up and go heavier; you can always throw it off, but you can't add wool you didn't buy.
How to actually use it in a power cut
A blanket's job is to trap the heat your body is already making, so use it as a layer, not a substitute for clothes. Put thermal base layers on first, add a hat, then wrap the blanket over the top and tuck it in so warm air can't escape at the neck and feet. Warm the core, not the room: gather everyone into one warm room, share body heat, and add a hot water bottle or hand warmers under the blanket for a real boost. Sit on it as much as under it — a wool blanket folded beneath you on a cold sofa or floor cuts the heat you lose downwards, the same reason campers use a sleeping mat. For the very old, the very young and anyone unwell, keeping wrapped and warm is a genuine safety measure, not just comfort: see our hypothermia kit and the older relatives winter kit.
Where it fits alongside your other warmth kit
Think of warmth in layers, cheapest and simplest first. A wool blanket and a foil emergency blanket do different jobs and you want both: the foil sheet is featherweight backup for the grab bag and the car, the wool blanket is the comfortable one that lives on the sofa and comes out the moment the power drops. Add a thermal sleeping bag if you want proper overnight warmth in an unheated house, base layers and a hat for the warmth you carry on your body, and a hot water bottle for a cheap, targeted heat source. None of these need power, which is the whole point — read staying warm in a winter power cut and what to buy before a winter storm for how they work together, and the 48-hour power cut plan for the bigger picture.
Care: keep it working for years
Wool is hard-wearing but doesn't like heat and agitation. Most wool blankets are best hand-washed or given a cool wool-cycle wash with a wool-safe detergent, then dried flat away from radiators and direct heat so they keep their shape — a hot machine wash or tumble dry will felt and shrink them. Air a blanket outside now and then rather than washing it every time; wool resists odour well. Store it dry with the rest of your winter kit, because damp storage invites moths and mildew — a sealed bag or box with a moth deterrent keeps a good blanket going for decades. Bought and cared for once, a proper wool blanket is genuinely a buy-it-for-life item.
The short version
Buy for the fibre, the weight and the size. Choose a clearly-stated pure wool, lambswool or high-percentage wool blend — not an acrylic "wool-look" throw — at 500 GSM or more for real power-cut warmth, and big enough to wrap and tuck. Keep it on the sofa where you'll actually use it, pair it with a foil emergency blanket for the grab bag, layer it over base layers with a hot water bottle when the heating's off, and wash it cool and dry it flat. See our wool blanket pick for a buyable, availability-checked option.
