The Chiller L/S shirt from Mountain Hardwear is might just be the coolest hiking shirt on the market – loaded up with Cool.Q Zero technology, this is about as chill as you can get in a long sleeve hiking shirt. The Chiller and I suffered through 75 miles of New Mexico sun and it’s definitely time to spill the beans on this awesome product.
Mountain Hardwear Chiller Shirt Features:
- Wrinkle-resistant, quick-drying and durable fabric
- Seams rotated away from pressure points for comfort under a pack
- Flip-up sun protection collar
- Zip chest pocket
- Sleeve roll-up tab for quick fit adjustments
- Colors: Grill (tested), White, Grey Green
- Weight: 9 oz
- MSRP: $110
My Experience
At the heart of the Chiller, we have a pretty classic backpacking sun shirt. Long sleeves, generous sun collar and a neutral grey color to fend off Mountain House spills. Where the Chiller really shines, though, is in its Cool.Q fabric; Cool.Q is Mountain Hardwear’s equivalent to Columbia’s Omni-Freeze technology (which we saw in the Freeze Degree tee) and it’s basically a water-attracting treatment that actively wicks the sweat off your body and into the fabric. This sounds pretty simple, but in practice the increased evaporation rates from this technology help the Chiller be noticeably cooler to wear than other hiking shirts.

This is the first time I’ve noticed a real, tangible difference with this sort of hydrophilic coating – I’ll tell you, from my personal experience the Chiller is quite a bit cooler than other sun shirts. It’s not something that I could give a numerical value to, but there’s no doubt that I was noticeably more comfortable with the sleeves down than in other shirts.
Complimenting the Cool.Q treatment are rows of tiny micropores under the armpits – these little guys, coupled with a lighter stretch fabric, keep the underarms cool and let a nice breeze through when you lift up your arms.

Overall the fabric is phenomenal – tons of stretch, yet still highly resistant to snagging. The shirt is definitely on the roomy side and I would recommend sizing down. The Chiller sits well under a pack and has a decent drop tail that doesn’t ride up; in the mean time, thoughtfully placed seams make pressure points a non-issue.
All of the little features that I like to see are present and functional: the single Napoleon pocket is roomy and its zip slides easily with one hand. The buttons don’t come undone (especially the ones under the waist belt) and the snaps for rolling up the sleeves stay put well. At 9oz the Chiller is light enough for me not to blink an eye, particularly since a good sun shirt is something that I never skimp on when counting ounces.

The Good:
- Cool.Q technology and micropores make the Chiller very comfortable in the heat
- Shirt performs well under a pack
- Single Napoleon pocket is deep, opens and closes easily with one hand
The Bad:
- More pockets would be nice
- Pricey
The Bottom Line
Ladies and gents, I don’t say this lightly: the Mountain Hardwear Chiller may just be the best long sleeve hiking shirt on the market right now. The fabric choice is really top-notch: it’s cool, resists snags and moves well in active conditions. The sizing runs very large so make sure to buy a size down. All things considered, this is one of the top garments of Summer 2013. Awesome job, Mountain Hardwear.
Buy now: Available from Backcountry.com