Why do some of my hand warmers seem to work reliably, while others are hard to activate and keep running when in my pocket?

Why can I get some of them up to 165F, while no amount of extra catalyst in the head won't get others anywhere north of 145F?

For years I have struggled with coming up with a definitive answer of how to improve the most ubiquitous of all the hand warmer units (think, “what am I going to probably buy from Amazon as I contemplate my cold hands I had on my last outdoor excursion”).

While I have not been able to come up with a hack that will improve the engineering of these units, I do have some personal observations that have given rise to my own subjective theories on this topic.

Hand warmer models shown in this presentation (top left to bottom right): S-Boston, Red Star, Jon-e Giant, Butterfly, Zippo. Note: The S-Boston is no longer in production.

00:13 Units that can go to 165F illustrated
01:15 The Red Star hand warmer – advantages
02:20 Jon-e Giant
02:45 Units I cannot get to heat above 145F
03:45 Theories: Thermal Flywheel effect and catalyst
05:35 constraints to move fumes from reservoir to catalyst head
06:00 'Cold Shock' defined
06:30 Catalyst heads compared
06:45 Catalyst heads, Zippo compared to Red Star
07:00 reservoir stacks compared to illustrate effect on fumes getting into catalyst (Zippo hand warmer and Red Star compared)
07:30 Considerations for the most suitable hand warmer for your pocket?
08:30 Reasons why the Red Star is preferred

Links:
Rebuild parts, order form:
https://forms.gle/yhcMy4Akuq9bdfTo7
Handwarmers S07E01: Why the Zippo Underperforms
   • Handwarmers S07E01: Why the Zippo Und...  

Handwarmers S04E10: The Red Star Handwarmer, memories of the Cultural Revolution?
   • Handwarmers S04E10: The Red Star Hand...  

Complete handwarmer Playlist:
   • Handwarmers