UnderWarmer

UnderWarmer is a disposable heated bodywarmer worn beneath your outer clothes. Its built-in heat packs activate when exposed to air, so getting it ready starts with opening the package. There’s no battery to charge. The company markets the lightweight, compression-style garment for cold-weather outings such as tailgating, hunting, hiking and camping.

Heat that starts when you open the package

UnderWarmer’s FAQ says the packs begin working once exposed to air. Keep the package sealed until you’re ready to wear it. Opening one to look at the garment ahead of your trip would start using its heat supply.

How it fits with your other layers

UnderWarmer has a close fit intended to hold its warmth near the body. The official store offers small, medium, large and extra-large sizes and suggests starting with your usual shirt size. For someone between sizes, the brand recommends sizing up so the garment isn’t too tight.

The FAQ says to wear a lightweight shirt or base layer underneath, then add clothing over it as needed. Allow for that light shirt when choosing your size.

A limited supply of heat

The company says an UnderWarmer provides about 12 total hours of warmth, with duration and temperature varying according to weather, activity and airflow. If you’ve only worn it for a few hours, its FAQ says resealing it in an airtight bag may preserve the remaining heat for later. The packs eventually harden after their heat is used up, and the garment is then discarded.

For regular outdoor use, plan on buying replacement garments as each one’s heat is used up. That’s a practical difference if you’re comparing it with gear you can recharge.

Where to buy UnderWarmer

ABC’s gallery identifies UnderWarmer in the October 7, 2026 episode “Diary of a Shark” and names Paul Schaefer and Bryan Schaefer among its presenters.

The official product listing showed a price of $14.99 USD when checked October 8, 2026. Use its size selector to see the options for your order, and review the delivery total before checkout.