Cotton long underwear stinks and stays damp. Merino regulates temperature, never smells, and lasts forever.
Why Not Just Buy the Cheap One?
Icebreaker's merino wool manages moisture and temperature naturally, preventing the bacterial growth that makes cotton base layers reek after one wear, requiring daily washing and degrading fiber strength. Merino also regulates heat without overheating; cotton traps sweat and loses all insulation when damp, leaving you shivering.
The Buy-Once Math
Buy five cotton base layers at $15 each to rotate because they smell horrible and need constant washing—that's $75 that wears out in three years as the fibers pill and thin. Icebreaker layers cost $80-100 but last eight years, smell fresh after two weeks of use, and regulate temperature better in any condition. You're paying the same for one pair that works versus five that fail.