Frequently Asked Questions

How does UnderWarmer work?
UnderWarmer uses built-in, air-activated heat packs to deliver convenient warmth to your core – no batteries, no charging. Once exposed to air, the built-in heat packs activate and provide warmth for hours. You simply remove it from its package and put it on. DO NOT OPEN the UnderWarmer® until ready to use.

Does UnderWarmer have an expiration date?
As long as the packaging is not compromised and remains properly sealed, UNDERWARMER can maintain its effectiveness for an extended period of time. While we have not established an official expiration date, we have successfully tested products that were 2–3 years old and found they still activated and produced heat. For best results, store your UNDERWARMER in a cool, dry place until you're ready to use it.

Why UnderWarmer instead of a heated jacket or vest?
UnderWarmer gives you reliable, air-activated warmth without batteries, charging or expensive heated gear. Just open it, put it on and stay warm. 

What should I wear under my UnderWarmer?
Wear a lightweight base layer or shirt underneath your UnderWarmer. Additional clothing can be layered over as needed. 

Can I take an unopened UnderWarmer anywhere?
Because it doesn't require charging, an unopened UnderWarmer can be stored with your cold-weather gear and activated when you're ready to use it.

How long does the heat last?
Each UnderWarmer provides about 12 hours of consistent warmth, making it ideal for all-day outdoor activities like hunting, football games, or working outside. Heat duration and temperature may vary depending on weather conditions, activity level and airflow. 

What size should I order?
We recommend ordering your typical shirt size. The UnderWarmer is designed for a close, compression-style fit to keep the heat close to your body. If you are in between, size up so it's not too tight. 

How many times can I wear the UnderWarmer? The UnderWarmer is designed as a convenient, disposable warming solution. However, if only worn for a few hours you can reseal in an airtight/ziplock bag and it can be used again. This can be done a few times. Understand that after 12 hours of producing heat, the packs will harden and the UnderWarmer is then disposable. Without a proper reseal, heat reactivation will not occur.

Do you offer free shipping?
Yes, we offer free ground shipping on orders over $25. No overnight shipping available.