Good product

Verified Buyer Reviewed by Tri guy from St. Louis on Thursday, February 15, 2018
Packs heat up quickly once opened, provide nice warmth in mittens even at zero degrees. However, 7 hours seems a bit optimistic; 3-4 hours is more like it. Take extras if you need several hours of heat.

I have had some older packs that were near or past the expiration date and those did not work too well, so they do deteriorate with time.
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