Yesterday I did an hour and a half ride in what I think is cold weather. Sunny, light breeze and 18 degrees F. To help keep my feet warm I used chemical heat insoles. I opened the package, activated them to warm and placed them in Sidi mesh shoes, used wool socks and neoprene booties. Feet were comfortable for about 30 min. and somewhat chilly for the rest of the ride. When I got home the insoles were cold. The package said that they are good for up to 5 hrs. What did I do wrong?

The pads need access to air to continue to work.

Personally, I find real winter cycling shoes work. I use Diadora Chilis, but there are other good makes.

Never used heatpads although we have a few around the house that were bought on Impulse. These are the ones that you re-energise by putting in hot water and when you want heat- you bend them. My wife used to work outside in all weathers and she used them as handwarmers.

But keeping wind and wet away from the feet works. Toe covers- better windproof shoes and windproof socks work. So does two pairs of socks with a plastic bag sandwiched between them. The other thing I have noticed is that socks containing cotton keep the feet cool--or cold in winter.

What brand did you get? I use Hot Hands Toasti-Toes foot warmers(advertised for 8 hours). BTW, foot pads are supposed to work fine in a limited oxygen environment. I use mine with sneakers(toe-clips) that aren't vented--likely be considered walking shoes, not running, and the toe warmers work fine. I have to use chemical toe warmers and hand warmers as my hands and feet get cold very easily.

I don't bike in the cold (too much snow) but I run until it gets below - 30. The best way I've found to keep your feet warm is to keep your feet cool. If you put hot pads in your shoes and they get warm enough to make your feet sweat, you'll be cold. The moisture sucks the heat out of your skin. I have a pair of shoes that are a size too big. When it gets cold, I wear a wicking sock (made of material that wicks the sweat away from your skin) next to my skin and then a double layer running sock over top. Put on a pair of wind proof shoes and I'm good to go.

I've had VERY variable results with chemical foot warmers. It may be brand dependent, but I haven't done enough research to tell you which ones work best.

It is true that they need access to air to work, but there should always be enough air in your boots to allow them to work - I don't believe that any of us wear boots tight enough to keep a minimum of oxygen from circulating into them.

On the other hand, I have wondered if TOO much air can limit their useful life - the basic reaction is oxidation of metal (iron powder, I think?), and surely oxidation goes faster in a well ventilated system as compared to one with comparatively stagnant air - (i.e. think blowing on a fire....). If you've got ventilation holes on the bottom of your Sidis, you may be blowing on the pads with a 15 MPH bellows. (or 20? you get the idea).

FWIW, I've been wearing these this winter:

https://www.cotswoldoutdoor-static.co...1101781010.jpg

(with powergrips, rather than with a cleted pedal). They're rated to -25 °F or so, but I don't think that the rating translates to cycling. Still, with these at 20 °F, my feet are absolutely comfortable for hours. At 10 °F, they start to get a little cold after maybe 90 minutes.

In our canoeing days, we used chemical heat warmers inside neoprene boots inside dry suits with booties with great success. The booties on dry suits makes a nearly air proof environment and we felt they actually lasted longer!
R&J

You might find my article on Cold Feet helpful ...

https://www.machka.net/whatworks/coldfeet.htm

Thanks all for the information. BTW BM, they were Graber brand warmers. I will try the suggestions and continue to experiment. They sure were nice at the beginning of the the ride.

It's certainly possible that the oxygen can get depleted inside a shoe or boot. It's not air tight, but without ventilation, no fresh air enters to replenish the O2 that's consumed.