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Warmth Factor, GSM, fit, and sizing explained for men, plus what to actually wear underneath. A practical guide to choosing a Hot Chillys base layer.
Merino absorbs moisture, synthetic repels it. That single difference decides drying speed, odor, durability and cost. Here is the honest comparison, and why Hot Chillys builds synthetic base layers by design.
Four decisions get you the right women's base layer: Warmth Factor, fabric weight, fit, and size. Here is how Hot Chillys rates each one, plus full size charts and why GSM alone will not tell you how warm a base layer really is.