The ultimate 'tip' for warm feet is - the 'Feater - The Feat Heater ' from Grüezi bag ! The magazine 'Cycle' reports in issue no. 1-2020 about the heatable, waist-high additional bag that fits in every sleeping bag. Here the report as .pdf for download: Cycle-Issue-No-1-2020 Page 75-Feater-The Feat Heater by Grüezi bag 'Feater - The Feat Heater Deluxe ' - the special present!