So far, almost all base layer recommendations hav...

So far, almost all base layer recommendations have been for Merino Wool. Last fall I wore Smart Wool on an October backpack hunt in Idaho and was really impressed with the comfort and performance.  Since then I have been doing a lot of research on Merino wool.

Originally the term merino specifically regarded the wool of Merino sheep reared in Spain.  However, due to the equivalent quality of Australian and New Zealand wool it now has a much broader meaning.  Merino sheep have the finest and softest wool of any sheep. Merino’s wool is finely crimped and soft with Staples 2.5 – 4 inches long and less than 24 micron (µm) in diameter. Basic Merino types include: strong (broad) wool 23 – 24.5 µm, medium wool is 19.6 – 22.9 µm, fine 18.6 – 19.5 µm, superfine 15 – 18.5 µm and ultra fine 11.5 – 15 µm. Ultra fine wool is suitable for blending with other fibers such as silk and cashmere.

High-quality merino performs in cold and warm weather.  There is a lot written about the advantages of wool for cold weather, however warm weather is where I was most surprised.  Wool naturally pulls water away from your skin and into the fibers up to 1/3 it’s weight.  In warm weather this moisture in the fibers causes an evaporative effect that actually cools the skin.

The key to Merino is understanding what you are buying.  I recommend only superfine merino for next to skin.  Superfine Merino 15 – 18.5 micron (µm) has no itch and is very soft and comfortable. I have heard complaints of Merino being itchy and uncomfortable.  If you put Medium Merino 19.6 – 22.9 µm next to your skin you may feel a slight itch due to the larger fibers and more importantly larger scales on the fibers that cause the itch.  I highly recommend next to skin layers with 17.5(µm) fabrics.  18.5(µm) fibers are more common for base layers due to the higher expense of 17.5(µm) fibers. From my testing it is worth the extra expense for 17.5 (µm) merino.

Read the contents labels carefully and buy only 100% merino wool.   Some fabrics include poly blends and lycra.  Lycra attracts water and will wear out over time.


  • Merino is excellent at regulating body temperature, especially when worn against the skin. It provides some warmth, without overheating the wearer. The fabric draws sweat away from the skin and is slightly moisture repellent (keratin fibers are hydrophobic at one end and hydrophillic at the other), allowing the wearer to avoid the feeling of wetness.
  • Merino can absorb moisture up to 1/3 its weight. Unlike cotton, it retains warmth when wet because it pulls the moisture away from your skin.
  • Merino is naturally anti-bacterial resistant, which causes the fabric to resist odor caused by sweating. This is a huge advantage compared to synthetic fabrics and ideal for extended backcountry hunts.
  • Merino is incredibly soft, due to finer fibers and smaller scales which eliminates the itch associated with regular wool.
  • Merino has an excellent warmth-to-weight ratio compared to synthetics and to other wools, in part because the smaller fibers have microscopic cortexes of dead air, trapping body heat similar to the way a sleeping bag warms its occupant.

During my research I have cultivated a relationship with the leading Merino supplier in New Zealand.  They work with several high-end Outdoor brands and offer some absolutely amazing fabrics.  We are working on the development a couple of new fabrics for KUIU.

It would be helpful to better understand what weight and style base layers you prefer?  My preference is a light weight 150-185 g/m2 next-to-skin and an expedition weight 200-240 g/m2 as the next layer in the system.  I prefer both of these shirts as a Zip-T to ventilate during a climb.

Thanks for the input and help.


This article has 14 comment(s)

  1. Benjie


    I like the direction that you are heading.

    Over the past few years i have become a big fan of merino wool. I wear mostly smartwool now.

    Here is another interesting tidbit about merino wool. I do a little bit of scuba diving and spearfishing not near as much now as i used to. but a few years ago i bought a new wetsuit for winter diving, that wetsuit is lined with merino wool. let me just tell you how much better and warmer i am in that suit over a strickly neophrene suit.

    i could go on and on, but buying that suit with the merino lining made me a believer, it kept me warm, dried amazingly fast. even after being under the water for 30 plus minutes after only a few minutes topside it was dry to the touch.

    i would keep it simple 2 weights both in zip t which prefer.

    • Jason Hairston

      Hi Benjie,

      I have not heard about this in wetsuits. I know Patagonia is putting merino in their stocking feet waders. Your comments on the Zip-T’s is well noted.



  2. ralph[Beau] Purvis

    I would want the 150-175 next to skin…zip-t [long]..camo to use in hot weather bow hunts as ‘the only layer’

    • Jason Hairston

      Hi Ralph,

      Thanks for your input. I think we are both on the same page for this next to skin piece. I too do a lot of early season, warm weather hunts in California and Nevada and can appreciate the need for the right weight in these conditions.


  3. Adam Casagrande

    I like the idea of a very lightweight layer and an expedition layer.

    I do like the idea of the zip t but I hate the high collar on my base layer that is why I typically go with the crew neck.

    Is there a way to do the zipper and not have the high collar.

    Camo and non camo options would be nice

  4. Tye Abell

    I’m certainly glad to see you’ve chosen merino wool, makes me a happy man.

    As for the shirts, I prefer my base to not have a zipper, as I don’t want the zipper rubbing my bear skin and irritating it, all other layers, the zipper is great. I also like to see a mid-weight layer to go along with an expedition layer. The mid-weight is great for mid season stand hunting when an expedition would be too much, or for wearing while glassing in somewhat cool, but not truly cold weather. For the bitter cold, the expedition would be great to put back on after humping it up to the glassing spot.

    That’s just my two cents, and having camo and non camo options would be great.

    • Jason Hairston

      Hi Tye,

      Your comments are well noted. If we do a Zip-T, I will make sure it is designed not to rub on your skin. Thanks for bringing this to my attention.



  5. Tony Mudd


    I could not agree more with the Merino wool comments.
    There is not a better material out there.
    The only down side that I have seen is the cost.


  6. Matt

    I like the two 3/4 zip idea. It might be nice to have a light weight t-shirt as well to stick with the line. Perhaps with a v-neck or something.

    Look forward to seeing what you come up with.

  7. Ray

    Last year in MT I used a 200 wt Icebreaker Mondo zip for my first layer and a Traverse as my second layer while elk hunting. It worked really well over a large range of temps but it never dropped much below freezing either. A few months back I got a 260 wt Icebreaker to replace the Traverse but I think it’ll be a little warm for the early season.

    Based on my experiences I think the weights you are looking at would work well over a broad range. I’d probably want something on the upper end of the ranges you have listed but it’s usually more cool then hot here. I’m really glad to see your considering wool.

    Another up side to the wool layers I’ve been using is that they’re naturally stretchy which is especially nice for pant layering. Also being stretchy it’s forgiving fit wise so I’d think you’d get few complaints from people not finding a size that worked well for them.

    • Jason Hairston

      Hi Ray,

      Thanks for your comments, they are well noted. Icebreaker makes some great product.


  8. Antonio Lara

    I use a merino top with a zip and it is awesome. I find myself using it all the time instead of a long sleeve T or just plain T. It really does have excellent odour control performance and the zip helps to control your temp as your activity levels go up and down.

    I have used merino base pants as well and my only worry with the pants is durability. I use them here in Australia on alpine hunts and we have a lot of balckberry. When I was walking with merino base pants, I found that they caught on the thorns a lot and hung me up somewhat, causing sevral small holes to appear. Part of the problem was that they were somewhat loose fitting and I think if they were more tightly tailored then they may have held up a lot better and brushed through the bushes rather than being hung out there to catch, if you get my drift.

    The top was ok though, as in the main you are above the leg grabbing thorns, plus I use the top near my home where we have a clothes eating bush called lantana and it is holding up well there.

    • Jason Hairston

      Hi Antonio,

      Thanks for sharing your experience with merino. There are two downsides with merino in my opinion. Price and durability, however you cannot have a shirt as comfortable as merino and not have a durability trade off. As far as price, it is what it is. $100+ for high quality merino base layers.


  9. Doc

    I like the idea of a 3/4 zip, however. Please, Please, don’t make the zipper as long as the Sitka Core shirts. I find it annoying when my shirt opens up that far. When the zipper on those shirts are open that much the collar on my neck flaps around while I walk, and if I’m using my shoulder strap for my rifle or if I’m wearing my shoulder straps for my binoculars the shirt will fall down to one side giving that 80’s cut off sweatshirt look. 4-6 inches of zipper length would be perfect, plus you would save extra weight!!!!!!