Summer running calls for lightweight shorts to keep you cool.  Mountain Hardwear’s CoolRunner shorts attempt to do lightweight one better, with fabric technology that actually cools you down as you run.

Mountain Hardwear CoolRunner Shorts Features:

  • Body fabric: 4-way stretch Ultralite plain weave, 86% polyester, 14% elastene
  • Lining: CoolQ Zero stretch softie jersey
  • Durable water repellant (DWR) finish
  • Elastic waistband with internal drawstring
  • Internal lining key pocket
  • Horizontal back center zipper pocket
  • Dual flank pockets
  • Seamless drawstring waistband
  • Mesh side panels
  • Weight: 4.8 oz (136g)
  • Available in three inseams: 7 (tested), 5 and 3-inch
  • Two color options
  • MSRP $65.00

mountain hardwear coolrunner shorts running

Cool Running in the CoolRunner Shorts

Lightweight?  Definitely.  Cooling?  Maybe.  That’s the short version of my experience in testing Mountain Hardwear’s CoolRunner shorts.  For details, read on.

First and perhaps most importantly, this is an extremely comfortable, lightweight, high performance short.  Overall weight of my 7” inseam version is a mere 4.8 oz, and the weight would be marginally less for the 5” or 3” inseam versions.

mounatin hardwear coolrunner side panels

The main fabric panels are very thin, with a small amount of stretch to provide full range of motion.  The ventilation panels effectively move moisture and improve air flow across the side panels and below the rear waistband.

The interior lining proved soft and comfortable against the skin for multi-hour runs, and the seamless waistband is especially appreciated when wearing a waist-mounted bottle carrier.  CoolRunners are also made with multiple pockets to stash small items during your long runs, but in my testing only the horizontal zip pocket and interior key pocket were highly functional – the flank pockets are too small to carry gels without bouncing out, and there’s no closure mechanism to keep smaller items like empty wrappers from working their way out over a period of time.

mouintain hardwear coolrunner side pockets

Seamless waistband and side stash pocket

So here’s the scoop with the fabric technology: on the interior lining, Mountain Hardwear uses an innovation called CoolQ Zero, which is billed as an active cooling technology.  If you look closely at the lining, you’ll see hundreds of very small circles in the fabric; each of them are filled with a sweat-activated cooling agent designed to lower the overall temperature of the fabric and accelerate the wicking process to help your body minimize heat and maximize energy.

When I read about the technology, I was thinking (and perhaps fearing) it would feel something like wearing one of those impact-activated cooling packs like you find in first aid kits inside your shorts.  The actual effect is much more subtle, and in my testing isn’t even a cooling sensation – rather, what you notice after a while is the absence of overheating or sweat accumulation.

The lining as well as the entire garment definitely remain comfortable during long duration activity, but is probably attributable just as much to the lightweight fabric construction as it is to the CoolQ Zero mechanism.  This may be one of those cases where you don’t worry too much about why something works so well – you just appreciate that it does.

The Good

  • Very lightweight
  • Highly comfortable for long runs
  • Outstanding temperature and moisture management

The Bad

  • Flank pockets aren’t highly functional
  • I’d love to see a 9” option available for taller runners seeking longer coverage.

The Bottom Line

Mountain Hardwear’s CoolRunner is a very nice summer running short, combining lightweight construction and fabric innovation to keep you cool and comfortable for high heat or high mileage.

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About Author

Donald is a physical therapist, ultrarunner, barefoot aficionado, and father of three with more than 20 years of experience in endurance sports. When he's not training for ultramarathons, he enjoys hiking or slacklining with his family in Monterey County, CA.

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