Merino Sheep (Photo: Jean / Just Chaos)

As part of our series of articles on clothing for winter obstacle course racing, we're going to focus our attention on the characteristics of Merino wool (as modelled by the Merino sheep above) and why it's worth adding a few garments to your running wardrobe. If you can afford it that is... unfortunately it's not that cheap.

Wool is an example of how clever nature can be sometimes. Although synthetic sports fabrics have come on in leaps and bounds in recent years, wool has been developed over millennia. It is naturally constructed with interlocking protein molecules, very similar to our own skin. Like our skin it is built to cool and heat the body, allowing its wearer (be it sheep or human) to survive in a whole range of conditions.

Smartwool vs regular woolI expect there's an alarm bell ringing for a lot of you - wool is itchy, right? Well, not always, that's why Merino wool is different. The wool of the Merino sheep has particularly thin fibres, which makes it really soft and stops it from being itchy at all.

Here are eight facts about Merino wool that make it perfect for sports clothing:

  1. When worn against the skin it regulates body temperature - providing warmth without overheating.
  2. It wicks moisture away from the skin as well as any synthetic sports fabric.
  3. Like cotton it absorbs water BUT unlike cotton it retains warmth when it's wet.
  4. It can retain 35% of it's own weight in water and still feel dry to the touch.
  5. It dries as quickly as performance synthetic fabrics.
  6. Wool absorbs and releases moisture through a natural chemical process - a bond is established between the atoms and, as a result, energy is released in the form of heat.
  7. It's soft not itchy.
  8. It's naturally stink-free.

Many of these characteristics are clearly good for running but we wanted to find out whether it would hit the mark when the going gets tough at obstacle course races. So, we ran a few questions past somebody who definitely knows his wool from his bull - Smartwool Product Development Expert Robert Thomas.

We’ve been reading up about the wonders of wool in winter conditions; how it wicks away moisture from the skin while keeping us warm. That’s a great feature for when we’re out on a regular trail run but when we’re obstacle racing we’ll get fully submerged in water. How would Merino wool react to that? Would it help to keep us warm in those conditions?

It's true that Merino does a great job wicking moisture, and moving sweat away from your body, helping keep you from feeling wet and clammy when you're active. But additionally, Merino insulates when wet. So, once you've submerged yourself and saturated your Merino apparel, it continues to insulate and keep you warm.

How is Merino wool better than wearing layers of synthetic fabrics?

wearing smartwoolMerino provides much better thermoregulation than synthetics, meaning a more stable core temperature for your body, allowing your body to focus on your activity, and not waste energy warming back up, or cooling back down if you overheat. It's been proven that wearing Merino actually helps athlete's maintain a lower heart rate, and lactic acid builds up at a slower rate. In addition, Merino is naturally antimicrobial (with no added nasty chemicals or metals) and won't stink after you've been sweating in it.

For general running in wet winter conditions, what combination of clothing would you recommend wearing?

If just running in wet winter weather, the athlete's goal should be to stay as dry as possible. Even though Merino insulates when wet, it is better to stay dry and only rely on that property of Merino if you start to get wet. Our preference is to wear a Merino baselayer on top, with a light, waterproof breathable shell to keep the rain off. The Merino will move sweat away from the body quickly, and a good shell will move it outside the athlete's microclimate while keeping the heavy rain off. We like Merino lined running tights (See our HyFi Tight, or Run Tech tight) and our PhD Run Light Mini socks with a waterproof running shoe.

With most races there are just small dips in water and there’s plenty of opportunity to warm up afterwards. However there are one or two that have massive amounts of very cold water over the course of a few hours – so the exposure can be quite severe. Many people have found that a mixture of merino wool base layers underneath Neoprene is a great combination. Would you agree with that, or would you recommend a different approach?

When obstacle racing, you know you will get soaked, so the strategy changes. Waterproof running shoes actually become a negative, as the water won't drain quickly once in enters your shoes. So avoid those, but keep the Merino socks on so your feet dont' get cold once wet. Starting with a Merino baselayer on all parts of your body will provide all of the benefits we've already discussed, and provide a nice layer of insulation as you build up your layering system. You mention using Merino under neoprene - which is a great strategy. The neoprene is an extremely good insulator, and relies on preventing water circulation from removing the athlete's heat by keeping warm water near the athlete. Adding merino underneath takes it one step further, as the merino further inhibits circulation, and it breathes better than neoprene before the athlete gets soaked. in fact, many high-end wetsuit companies rely on merino as a lining material for wetsuits, because it works so well. (See Pinnacle Aquatics and Oceanic for reference)

Thanks Robert!

I've enjoyed looking into the science behind Merino wool. Before now, I've only really known that it feels good. Hopefully it's been interesting to you too! Stay tuned because next week we'll be testing a range of Merino products - baselayers, running legins and long sleeve running tops.

Check out the other articles in our winter clothing series: Video episode one featuring the thermal rash vest | Smartwool compression socks test

Thanks to Jean for the Merino sheep picture above and Smartwool for the fibre and garment pictures.

For more news , tips and info about obstacle course races and mud runs. Follow Mudstacle on: Twitter, Facebook and Youtube.


  1. Everyone loves what you guys tend to be up
    too. This kind of clever work and reporting! Keep up the great
    works guys I’ve added you guys to blogroll.


Please enter your comment!
Please enter your name here

This site uses Akismet to reduce spam. Learn how your comment data is processed.