Do Emergency Blankets Really Work? A 10°F Field Test With a Surprising Winner

Ten degrees Fahrenheit is where cheap gear stops being a minor discomfort and becomes a medical event. Ivan the Veteran, a camper of 50-plus years, put four emergency covers through that cold. A cheap contractor trash bag did something the expensive reflective blankets couldn't, and the winner came with one serious problem nobody talks about.

The Four Covers, and the 90% Claim

These are not one product category. A space blanket is metalized polyethylene film, thinner than a receipt, with no closure or structure. A SOL Emergency Blanket is a tougher brand-name version with tie-out points. An emergency bivvy is a reflective bag you climb into. Contractor trash bags are thick polyethylene drum liners with no reflective coating.

The packaging says a reflective blanket "reflects 90% of your body heat." That describes reflectance of radiant energy, not how much total heat loss it prevents. A reflective surface bounces back only the infrared reaching it, in a straight line, across an air gap, while clean and dry. Press the film against your jacket and you are testing a plastic sheet, not a reflector. Ivan explains why that gap between marketing and physics matters.

Four Ways Body Heat Leaves

No single cover handles all four channels of loss:

1. Radiation. Skin emits infrared to colder surroundings — the only channel reflective film targets.
2. Convection. Moving air strips the warm boundary layer off your body. Still air insulates; moving air steals.
3. Conduction. Contact with snow, wet ground, or rock pulls heat out fast. The fix is insulation beneath you.
4. Evaporation. Sweat and breath carry heat away, and wet skin loses it far faster than dry.

Reflective blankets lead on radiation. Enclosed shapes lead on convection, sealing the openings a flat sheet leaves at neck and feet. None lead on conduction, so ground insulation stays separate gear. All struggle with evaporation in proportion to how well they seal.

Why the Cheap Bag Beat the Reflective Blankets

Its advantage is not magic and not reflection. It is enclosure. You climb in, the opening gathers at your shoulders, and the wind is gone. That removes convective loss at every edge at once and traps still air — and still air, not shiny film, is the real insulator here. It is also tough enough to be sat on where mylar tears, and cheap enough for real redundancy.

A reflective sheet works only while the shiny face turns inward across a gap; once it touches your clothing the gap collapses. Ivan's summary is the honest one: a cheap contractor trash bag did something the expensive reflective blankets couldn't. Between reflection and enclosure, enclosure won.

The Winner's Serious Problem: Condensation

The winner in this test was the approach that traded breathability for heat retention, and its serious problem is condensation. That trade isn't a defect — it is the bill for the win.

All night you release water vapor through sweat and breath. A non-breathable barrier has nowhere to put it, so it hits the cold inner surface, condenses, and runs into your base layer. Now you are wet inside a sealed envelope at 10°F. Water on skin pulls heat away roughly twenty-five times faster than air, and damp clothing loses its insulation. Reflection addresses none of it: once wet, your dominant losses are conductive and evaporative.

That is the wet-cold trap — the cover that keeps heat in also keeps moisture in, and in cold weather wet means dangerously cold. It is the theme in the viewer comments on Ivan's video, where people describe bags building condensation and recommend rotating them or layering them inside-out to move the wet surface off. Manage it by venting the opening, changing out of damp clothes, and sleeping in a dry hat and socks — the discipline in our guide to cold-weather clothing layering systems.

What to Actually Carry

Don't buy bags and skip the blankets — they answer different questions, so carry both. A reflective sheet is an ultralight windbreak, radiant layer, and visible signal panel. An enclosed bag stops convection when the wind picks up. Ground insulation is the piece people skip: without something between you and the snow, no cover performs.

Weight is the fair counterargument: a contractor bag weighs several times what a mylar sheet does, so you can carry four to six sheets for one bag. Thin sheets suit a hiking pack; bags suit a vehicle kit. Build it before the weather turns — see our winter car survival kit guide. Ivan's own recommendation is in the video above.

Key Survival Takeaways

• Enclosure beats reflection. The contractor bag outperformed the reflective blankets by stopping convective loss, not by bouncing infrared.
• The 90% figure covers radiant energy only — nothing about ground conduction, wind, or sweat.
• Ground insulation is separate gear — no cover here protects you from cold ground.
• Condensation is the hidden cost. Wet plus cold is how hypothermia starts.
• Vent and change. Never seal yourself in already sweating.
• Carry both — mylar for weight, an enclosed bag for weather.

Related Gear and Emergency Supplies

The four categories worth having on hand:

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Frequently Asked Questions

Do emergency blankets really reflect 90% of body heat?

Not the way shoppers read it. That figure describes how much radiant energy a clean, dry surface bounces back across an air gap. You also lose heat by convection, conduction, and evaporation, and a sheet pressed to clothing reflects little.

Will a trash bag really keep me warm?

Yes, meaningfully warmer than nothing, because it is a windproof envelope that traps still air — which is why it outperformed the reflective blankets on retention. But it generates no heat, insulates nothing from the ground, and traps moisture.

How do I stop condensation in a bivvy or blanket?

You can't eliminate it, so manage it: vent the opening, change out of damp clothing, and reserve dry hat and socks for sleeping.

Which is better for a winter car kit, mylar or a bivvy?

Both, because they fail differently. Mylar is nearly free in weight and doubles as a signal panel but tears and needs an air gap. A bivvy or bag takes reuse and closes wind but accumulates condensation.

The Bottom Line

Emergency blankets do work — just not the way the packaging says. What keeps a person alive through a cold night is enclosure, dry insulation, and ground separation, which is why a few dollars of contractor bag outperformed gear costing many times more. The winner earned its win and came with a warning: seal out the weather and you seal in the wet, and wet is what gets people killed.