The system is built on two ideas that work in every climate on earth.

First: merino wool as the only base layer fabric worth packing. It regulates temperature in heat and cold, resists odor for days of wear, and replaces the need for a full wardrobe of backups.

Second: a three layer system, base, mid, and shell, that adapts to any destination by changing one piece at a time instead of your entire bag.

Combine both with the carry-on only method inside this guide, and you can pack for two weeks, two climates, or two continents in a single bag, every time.