“BEST HIGH-TECH SKI GEAR FOR 2018 and 2019" - CNET, December 2018

When your phone gets too cold its battery drains faster and if it's really cold, it might even shut off.  That's where the Phoozy ($30) comes in. 

A simple sleeve or "capsule" for smartphones, the Phoozy has a Chromium Thermal Barrier Shell and SpaceTech Penetration Layer, as well as a bit of velcro to keep it closed at the top. That will help keep your phone warm on extra cold days and help preserve battery life. It will also keep your phone from overheating.

Read more here.