Under Armour ColdGear vs Smartwool: Synthetic or Merino Wool Base Layer?
Under Armour's ColdGear base layer is synthetic — roughly 78-87% polyester with elastane — built for fast drying and moisture-wicking during high-output activity. Smartwool's base layer is 100% merino wool, a natural fiber with a genuinely different set of trade-offs: it dries slower, but resists odor for multiple days of wear and doesn't shed plastic microfiber in the wash.
Quick answer: Under Armour ColdGear base layers are synthetic (roughly 78-87% polyester), drying faster but shedding microplastic fiber in the wash. Smartwool's 100% merino wool base layer resists odor for multiple days of wear and biodegrades at end of life, but dries more slowly.
Winner: Smartwool Classic Thermal Merino Base Layer Crew
For a single hard workout followed by an immediate wash, Under Armour's synthetic fabric dries faster and costs less at full price. For multi-day wear — travel, camping, backpacking — merino wool's natural odor resistance means you can wear it several days before it needs washing, and it biodegrades at end of life instead of persisting as plastic fiber.
Under Armour ColdGear Base 4.0 Crew
Under Armour
- ✓Genuinely fast-drying and moisture-wicking for high-sweat activity
- ✓Stretchy 4-way fabric construction
- ✓Well-established, widely available performance-apparel brand
Smartwool Classic Thermal Merino Base Layer Crew
Smartwool
- ✓Genuine 100% merino wool construction from a well-reviewed apparel brand
- ✓Naturally temperature-regulating and odor-resistant across multiple days of wear
- ✓Frequently discounted close to this price from a $115 list
Frequently Asked Questions
Does synthetic clothing really shed microplastic in the washing machine?
Yes — synthetic fabrics like polyester shed small plastic fibers during washing, which is a well-documented source of microplastic entering wastewater. Natural fibers like merino wool don't have this issue since they biodegrade instead.
Why does merino wool resist odor better than polyester?
Wool fiber has a natural structure that absorbs moisture vapor and has some inherent antimicrobial properties, which slows the bacterial growth that causes odor. Synthetic fibers don't absorb moisture the same way, so odor-causing bacteria build up faster on the surface.
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