Pre-juane cycling.

Merino wool has been a part of cycling for longer than the color yellow, and few contemporary brands know how to manipulate that venerable material better than SmartWool. The PhD Knit Arm Warmer is the quintessential wool cycling sleeve, combining everything we love about merino (anti-odor properties, the ability to stay warm even while damp) with some synthetic materials that add an element of stretch-and-return.

The arm warmer is a cycling staple that's well-suited to those pre-dawn departures that require protection that you can shed as the day warms up. Elbow articulation allows for added stretch, and welted cuffs at either end help maintain coverage.

  • A classic knit arm warmer
  • Built to flex at elbow
  • Cuffs keep warmer in place without binding
  • Merino wool is the first high-tech cycling fabric
  • Reviews
  • Q & A

Poor Sizing!

  • Familiarity: I returned this product before using it

I'm not certain who these are made for, but they aren't for this petite cyclist. They are too short and I have short arms as I'm only 5' 4" and a slender 118 lbs.. I ordered the XS/S and they fell about 2" above my hand and the wrist was so wide it gaped. The upper arm fit great, but the design that would align with the elbow didn't come close. I love Smartwool products, but not these. I'm so disappointed as I've been looking for a lightweight wool arm warmers to replace the wonderful Ibex pair I had. Sadly, they have lost their elasticity after years of use.

Is this a single arm warmer, or a pair of arm warmers?

Hey Jeffery,

It is a pair.

Sizing way off

  • Familiarity: I returned this product before using it

I'm 5'10", 140 pounds, and have normal length arms for my height. I bought a size L/XL. They are way too short, unless you're looking for "elbow warmers", which is really a shame since the quality of the material is great.

Wool is the way to go!

  • Familiarity: I've used it several times

Bought these on sale, best $12 I've ever spent!! They keep you warm without making you too hot if the temperature goes up. Super breathable and comfortable, a great spring, summer, fall arm warmer. I don't think they'd be warm enough for anything below 50... Fit is good, I got a S/M (I'm 5'3", 120lbs) just be sure the little "smart wool" logo is down by your wrist. They did stretch slightly after about seven uses, but tightened right back up after a wash. Been using them frequently!

Wool is all I buy

    I bought these for Leadville 2017. I had them on the entire race. They kept me warm on columbine and cool through out the rest of the day. 70° to 40° with occasional rain. They fit a little tight on me ebut I have bigger arms than the typical cyclist.

    Great gear

    • Familiarity: I've used it several times
    • Fit: Runs small

    these run a little small but they do stay in place Me I love arm warmers

    Awesome (when you wear them right)

    • Familiarity: I've used it several times
    • Size Bought: S/M

    These are great! I love that they keep my arms warm without making me overheat while running. They also don't seem to hold on to odors at all. My first run with these I hated them and lost circulation in my forearms, turns out I just had them upside down and now they feel great! Make sure the little SmartWool dude is standing right side up and near your wrist and they'll be far more comfortable.

    Can't go Wrong

    • Familiarity: I've used it several times
    • Fit: Runs small
    • Size Bought: L/XL

    Essential for those who have arm pain arthritis related symptoms .. not to mention very warm and comfortable wool (the merino). Started using it after my elbow injury puts the winter at ease especially skiing , great for business wear as well. good stuff

    fall rides

    • Familiarity: I've put it through the wringer
    • Size Bought: large

    those chilly days or nights you need a little extra warmth these babies to the job

    Wore out my first pair!

    • Familiarity: I've put it through the wringer
    • Fit: True to size

    These little things are a great value. Small enough to stash in rear pockets for when the weather cools off during your ride. These keep the wind off your skin and help keep your arms warm. Love them.

    Wool Power

    • Familiarity: I've put it through the wringer
    • Fit: True to size
    • Size Bought: L/XL

    I love wool. I wear wool whenever possible and appropriate. There aren't a lot of affordable wool cycling pieces out there, but this is one of them. It does a great job of keeping you warm on chilly morning rides and doesn't overheat you when the sun comes up. Highly recomended.

    Too tight!

    • Familiarity: I returned this product before using it
    • Fit: Runs small

    According to the sizing guide these should have fit me, but they were so tight that they cut off circulation when I bent my elbows. There's no way I could use them.


    • Familiarity: I gave it as a gift but have feedback to share
    • Fit: True to size

    Gifted to a friend. She says they look great, but they are so itchy she can't wear them. Will be returning.

    Good Product, not for Biking

      these arm warmers work great for most aerobic activity. the merino wool feels awesome and does a great job or providing warmth while wicking moisture. they don't provide as much wind protection as other materials though. they also don't have any water resistance, though they do dry quickly.

      great for running/hiking, go with something else for biking.


        lightweight, yet very warm for my early morning bike rides - as my arms are always the coldest part of my body at 6am. fit snug but not constricting.