You can't make the day any cooler, but you can wear the women's REI Co-op Swiftland long-sleeve T-shirt—it cools you with microventilated SwiftTex™, a fabric so airy and light it's barely there.

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If you like running long trails on warm days, you'll love the men's REI Co-op Swiftland T-shirt—it's made of microventilated SwiftTex™, a fabric so airy and cool it's barely heavier than the breeze.

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Forget the heat and focus on the fun. The women's REI Co-op Swiftland short-sleeve T-shirt is made with microventilated SwiftTex™ fabric that's so airy and cool you won't even notice it's there.

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You can't outrun heat, but you can run cool in the women's REI Co-op Swiftland short-sleeve T-shirt. It's made with microventilated SwiftTex™, a fabric so light and airy you barely know it's there.

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For afternoons pedaling in the city or up and down hills through the countryside, the women's Marmot Switchback long-sleeve shirt is made in a lightweight rib-knit fabric that has an extra-soft feel.

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Made for the modern hiker who takes a fresh, unconventional approach to life, style and the trails, the Marmot Syrocco shirt breathes easily and dries fast, so you stay cool from trailhead to brewpub.

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Whether you're exploring new trails or city streets, the men's O'Neill TRVLR Traverse shirt will keep you cool, covered and comfortable in a lightweight, sun-protective fabric that wicks moisture.

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Enjoy your day in comfort, however your move through the trees. Soft, breathable and moisture-wicking, the women's Arc'teryx Taema Crew shirt is a great pick for off-road runs and hikes.

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For the intensity that bike parks and freeride adventures provide, the women's Mons Royale Tarn T-shirt is fast wicking and offers increased durability thanks to its Merino Shift fabric.

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With a looser fit and fabric that wicks away your hard-earned sweat, the men's Under Armour Tech 2.0 T-shirt is a go-to for high-intensity workouts and hot-weather adventures.

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Lightweight and breathable, the men's Icebreaker Tech Lite II Crewe T-shirt is a versatile top that's ready for it all. It helps regulate your temperature, wicks sweat and even stays warm when wet.

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A super-versatile tech tee, the women's Icebreaker Tech Lite II Crewe short-sleeve T-shirt is ready for it all. It helps regulate your temperature, wicks away sweat and even stays warm when wet.

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A versatile adventure tee, the women's Icebreaker Tech Lite II Nature Celebration Scoop T-shirt lets skin breathe, provides stretchy comfort and keeps you cool when it's hot, warm when it's not.

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A versatile adventure tee, the men's Icebreaker Tech Lite II Polar Paddle T-shirt lets skin breathe, provides stretchy comfort and keeps you cool when it's hot, warm when it's not.

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