How to improvise a hypothermia wrap from standard hiking gear

Most people picture hypothermia treatment as something that happens in a hospital — warmed IV fluids, a Bair Hugger blanket, a monitor beeping reassuringly in the background. In the field, days from a road, none of that exists. What you actually have is a stalled or collapsed group member, a pile of gear scattered across the group, and however much daylight is left. The good news is that the single most effective field intervention — stopping ongoing heat loss — doesn't require any of the hospital equipment. It requires insulation, a vapor barrier, and getting the sequence right.

Why the wrap matters more than active rewarming

A cold, exhausted hiker loses heat through four routes: conduction into whatever they're sitting or lying on, convection from wind moving across wet or exposed skin, evaporation from sweat-soaked clothing, and radiation from bare head and neck. Of these, conduction into the ground is the one people consistently underinsulate — it's intuitive to throw a jacket over someone's shoulders and easy to forget that a wet, cold hiker is losing just as much heat into the ground or a foam mat as they are to the air.

In the field, your job is to stop all four routes before you worry about actively adding heat. A hot water bottle tucked against someone who's still lying on cold ground, in wet clothes, with their head exposed to a 20-knot wind is being warmed with one hand while being cooled by three others.

How gently you handle the patient matters as much as how you insulate them — and the trigger for switching into "gentle handling mode" is a clinical sign, not a thermometer reading, because you won't have a reliable core temperature in the field anyway. The moment someone moves from simply cold and shivering to confused, uncoordinated, or no longer shivering at all, treat them as moderately hypothermic and start minimising movement from that point — don't wait for a specific number. The heart becomes progressively more irritable as core temperature falls through this range, and by the time someone is unmistakably cold and confused, rough handling, being made to walk, or vigorous limb-rubbing can trigger a lethal arrhythmia. Cold blood pooled in the limbs returning suddenly to the heart's core — through exercise, being stood upright, or brisk massage — can itself drop core temperature further and precipitate arrest, a phenomenon known as afterdrop or rescue collapse.

What you're actually building

A hypothermia wrap has four functional layers, built from the outside in, sourced entirely from group gear. None of it needs to be purpose-made — a contractor bag does the job a commercial vapor barrier bag does; a stack of empty packs does the job a foam mat does when mats run short.

Building it, in order

Get them off the ground and out of the wind before anything else. Even a rough windbreak from packs and a single foam mat under a sitting patient buys you time to organise the rest properly. Don't wait until you've built the full wrap to deal with the two biggest and fastest sources of ongoing heat loss.

Change wet clothing for dry, if it's safe to do so. Wet base layers next to skin are actively working against you. If you can get the patient somewhere sheltered enough to change — even just a base layer and socks — do it before you wrap. If conditions are too exposed or the patient is too far gone to safely undress and redress, don't delay the wrap to force it; get the vapor barrier over the wet clothing instead and change layers once you're sheltered.

Lay the ground insulation first. Mats, then packs, then a groundsheet or footprint — build this before the patient lies down on it, not after.

Wrap the vapor barrier directly around the patient, over dry clothing where possible, leaving the face clear. This is the layer people are most likely to skip because it isn't obviously "warm" — it's doing its job by stopping the insulation around it from getting wet, not by adding heat itself.

Build the insulation bulk over the top — sleeping bags nested or layered, spare jackets packed into any gaps, particularly around the neck, armpits and groin where a lot of heat escapes through poorly sealed gaps. Cover the head and neck with a spare hat or buff.

Seal the outer shell around the whole bundle — tarp, flysheet, or a combination, tucked and weighted so wind can't get underneath it. This is the layer that turns everything inside into a functioning system rather than a pile of warm gear losing heat to a 20-knot wind.

Add a heat source at the torso, not the extremities. Chemical heat packs or a water bottle filled with warm — not scalding — water, placed at the axillae, groin and either side of the chest or upper back, transfer heat fastest at these points because of the major blood vessels running close to the surface there. Never place a heat source directly against bare skin — wrap it in a sock or a layer of clothing first, and check the skin underneath periodically. Hypothermic patients often have reduced peripheral sensation and circulation, which means they can develop a significant burn from a heat pack before they'd normally feel it.

A rough guide to how cold is too cold

Wilderness medicine uses a simple field staging system, because you're very unlikely to have a thermometer that reads accurately below 34°C, let alone the time to use one properly. It's built entirely around what you can observe: is the patient shivering, are they making sense, are they still moving under their own steam.

Mild (conscious, still shivering): the patient can generate their own heat and protect their airway. Warm, sugary drinks and food are appropriate here, alongside the wrap, and gentle self-directed movement is fine.

Moderate to severe (confused, uncoordinated, or shivering has stopped): this is a different problem. Shivering stopping is not a sign of improvement — it usually means the body has run out of fuel to generate heat. From this point, no food or fluids by mouth if there's any doubt about their ability to protect their airway, no exercise, minimal handling, and horizontal transport if you're moving them at all. This is squarely an evacuation, not a "warm them up and continue" situation.

The wrap doesn't change based on stage — you build the same system either way — but how you handle the patient inside it changes considerably, and getting that distinction right is arguably more important than any individual layer of the wrap itself.

What the wrap isn't

A hypothermia wrap buys time. It doesn't reverse significant hypothermia on its own, and it isn't a reason to delay evacuation while you wait to see if the patient improves. Build it, get a heat source in, keep the patient horizontal and still, and get help moving at the same time — not sequentially. In a genuinely remote setting, the wrap is what keeps someone stable enough to survive the hours it takes for evacuation to reach them, not a substitute for that evacuation.

It's also worth normalising within your group before anyone needs it. A hypothermia wrap built for the first time, under pressure, by people improvising the order of layers on the spot, works far worse than one built by a group who has practised it once on a cold afternoon with nothing at stake. It costs an hour of a trip to run through it properly, and it's an hour that pays for itself completely the one time it's needed for real.