Phone Cozy

[David D]

A phone’s lithium battery capacity gets degraded temporarily by cold (~ 50% @ -20C)

As an experiment, I made a reflectix cozy for my iphone11 and was very happy with how well it worked @ -13C.  Bluetooth worked, barely any battery degrade, it’s cheap, light and fits easily in pocket.

Next step is to test below -20C with wifi on to generate some heat and see how far this concept can be pushed.

I haven’t seen this idea before so thought I’d share.  LMK how it works in Alaska! :)

[MJ H]

I have a similar thing that I bought at REI. Your way would be cheaper and fit better in my pocket, I think.

[David D]

With DIY this is a perfect custom friction fit, no tooling around in the cold or it slipping out.  I think its better than store bought options:

Decathlon

Phoozy

Phoozy2

 

[Philip Tschersich]

Where are you carrying your phone that it is getting so cold? If it is in a pocket, the minimal R value of the cozy is shielding the phone not only from the outside elements, but also from your body heat. A cozy with a double layer of insulation facing out and little/none facing you would probably be a more efficient use of material.

[David D]

In my pocket.  I hike down to -25c or less sometimes, and usually for 5 to 8 hours.  Just leaving in pocket with no insulation and the phone will auto shut down from cold temp.  I’ve been resorting to putting it in a sock, in a thin bum bag over my belly and under my mid layer but it’s inconvenient to access.  Ditto with tossing hot hands in there, it’s all fussy.  When it’s that cold, simplicity is valuable

I considered that it’s shielding from my body heat when in the cozy but expect it’s self heating trapped by the cozy to more than compensate.  It’ll depend on what radios I leave on to generate e-heating, more experimenting ahead. It was definitely warmer in the cozy after a 3 hour test hike at -13c with just Bluetooth on vs naked in my pocket

Maybe the double layer out, pantyhose in would insulate better but would be much less durable, harder to use in the field and harder to make.  I’m open to ideas how to address those.

[Philip Tschersich]

I can’t tell what you are using to join the mylar bubble wrap panels, but if it’s packing tape or something similar, just cut a rectangle out of a heavy plastic bag and use that for one side. If you wanted something more rigid that held its shape better, you could use a slightly stiffer piece of plastic like those really thin cutting boards. I use those for stiffener material with decent results. But if you don’t think your body heat is contributing much, this would all be moot anyway.

[David D]

Thanks for the idea.  I have scraps of clear vinyl tablecloth that might work.   If it doesn’t stay warm enough at the coldest temps, then I’ll give this a shot.

That’s the beauty of reflectix, buy a roll and experiments are cheap and easy.  Bought it to make double walled Nalgene cozies

I use reflectix tape which is a flexible and durable aluminum tape with a long lasting backer as it’s meant for house construction.

[Brad W]

I like this. I may make a slightly bigger pouch for my batteries and throw a hand warmer in there also.

 

[AK Granola]

I have a zippered phone pouch on a strap that I use in winter and wear around my neck. It rests on my chest between base layer and fleece. Easy to pull out as needed and stays warm. It has a separate pocket I can put a chemical toe warmer into if needed but I’ve only used that once. Even at minus 30F the phone does fine close to my body. Doesn’t take long in the open air at that temperature though, to freeze and fail utterly.  I purchased it on Etsy. I’ll post a pic if anyone is interested.

I don’t think any insulation on its own will help a phone much since it isn’t making any heat and cold will soon defeat the insulating layer.

[David D]

I went that route using a bag on my belly under my mid to hold my phone, and it works.  Now experimenting with something more convenient and that doesn’t let cold air in under my mid

The phone does generate its own heat if left on in the reflectix.  Bluetooth was enough @ -15C.

Hope having it search for wifi is enough at -25C, without draining battery.  Tests ahead, watching the weather

[Brad W]

@AK please post a link. Also, it doesn’t bother you having that weight pull on your neck?

When raining I keep my phone in the front pocket of my Hill People kit bag. I have not measured temps but it’s usually under a wind shirt or rain jacket in the winter.

[AK Granola]

The weight of the phone on a neck strap is barely noticeable. I frequently carry binoculars though, much heavier than, so I’m used to it.
this is a slightly different bag but same maker. The bag was shipped to me from Romania. High quality make and zippers as well as the strap.

[David D]

Also check the 3 I posted earlier, the Decathlon one is $12 Can

[David D]

Progress report

TLDR: it just works!  Weight, 11g

Over 6 hours @-15C phone in pocket in the cozy tracking my route in real time, GPS worked without a hitch, battery consumption was the same as summer & the phone didn’t feel like an iceberg.  Bonus points: it was easy and natural to slide the phone in and out using mitts, and it’s multi use, protecting the phone when I dorked and dropped it (a few times)

[Author]

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