With two thicknesses on offer, Pearl Izumi has both a thermal and lightweight base layer for whatever Mother Nature has in store. With the right mid and outer layers, both the thermal and s standard long-sleeve base layers have allowed me to stay warm and comfortable on cold rides.

Pearl Izumi Merino Wool Long Sleeve Base Layers Features:

  • Available in thermal and non-thermal models
  • Features polyester-backed Merino wool
  • Thermal model is thicker and warmer (obviously)
  • Thumb loops to prevent bunching
  • Form fit
  • Weight: 235 grams (thermal) / 145 grams  – large, actual
  • MSRP: $90-$110
Pearl Izumi Merino Wool Base Layers Review

Lightweight on the left and thermal on the right.

Baaa Baaa is Goood Goood

When it comes to Merino wool, I’m undoubtedly a fanboy. It comes blended with polyester and other materials to maximize the benefits (warm, natural, anti-stink) of Merino without all the drawbacks (stretched-out, saturated, itchy). As such, most Merino base layers feature a comfortable polyester layer next-to-skin for comfort and wool on the outside. That’s the formula that Pearl Izumi used with their latest wool base layers — and it works.

Over the past year, I’ve been testing both the lightweight Merino Long Sleeve Baselayer and the Merino Thermal Long Sleeve Base layer. There are good and bad points of each, but, as you’ll see, I much prefer the lightweight base layer.

Pearl Izumi Merino Long Sleeve Base Layer Review

My typical layering for a ride in the upper 30’s.

Both varieties feature stretchy thumb loops that come in handy when adding outer layers on top. Kudos for the inclusion here, without which, I’d have sleeves bunched at the elbows every time I put on an outer layer and that’s a downright terrible experience. You’ll notice that the overall cut of these base layers is very basic. There are no body-mapped panels, but instead, you just get a simple cut and unsophisticated fit. The lightweight Merino base layer (mostly due to the lighter fabrics) does fit better overall with a smooth, streamlined fit. The thermal flavor (due to the thicker fabrics) doesn’t fit as nicely and tends to bunch up.

As far as warmth goes, certainly, the thermal base layer is warmer overall. That’s both good and bad. If you are bike commuting or generally riding at a light tempo, it’s okay. But, if you’re really pushing the pace and working hard, it’s just too thick for my tastes. I prefer a succession of layers to expel moisture and provide warmth. With that, I much prefer the lightweight Merino base layer. It allows me to add the proper mid and outer layer, as needed. I get next-to-skin comfort, excellent breathability and solid anti-stink properties with the added ability to then opt for different varieties of mid and outer layers to suit the weather and my chosen ride.

Pearl Izumi Merino Long Sleeve Base Layer Thumb Loop

Those thumb loops come in handy and keep your sleeves from bunching up.

While you can certainly cut off the tags, I love that Pearl Izumi chose to sew the tags on the outside. Because of that, I haven’t thought about cutting them off because I don’t even notice they are there. As far as fit goes, I’ve been testing the size large in both base layers. I typically wear medium tops/bottoms in Pearl Izumi, so my suggestion is to size up with these and you’ll have a snug, but not sausage-tight fit.

Fit: I’m 5’11” and 170 lbs and I wore the size large in both base layers.

The Good

  • Merino wool is a wonderful base layer
  • Soft material next-to-skin is comfortable — even when saturated
  • Thumb loops keep sleeves in place when adding layers
  • Lightweight base layer allows for proper mid/outer layering
  • Tags are sewn to the outside
  • Wide, crew neck gets out of the way of jersey/jacket collars
  • Can wear it multiple times before it needs washing

The Bad

  • Thermal base layer is too thick for proper layering
  • Unsophisticated fit (not body-mapped and is mostly noticeable with the thermal model)

The Bottom Line: Pearl Izumi Merino Wool Base Layers

Merino wool, when blended with other materials, is durable, warm and comfortable. I’m a fan. Here, Pearl Izumi has chosen to offer two weights of Merino with their base layers. For me, the easy choice is the lightweight base layer, but if you ride in cold (sub-30 degrees) weather regularly or don’t put off a ton of heat, the thermal one may be worth exploring. The cut could be more body-mapped, but again, the lightweight one fits nicely under a variety of bibs and mid/outer layers.

Buy Now: Available from PearlIzumi.com

About Author

A native of the Pacific Northwest, Jason quickly developed a love for the outdoors and a thing for mountains. That infatuation continues as he founded this site in 1999 -- sharing his love of road biking, mountain biking, trail running and skiing. That passion is channeled into every article or gear review he writes. Utah's Wasatch Mountains are his playground.


  1. I definitely agree with what you wrote. The thermal version is effective at being warm for sure. The non thermal has that luxurious feeling of a nice merino baselayer, but for bikes. The short sleeve non thermal is pretty nice too. It really makes a normal warm weather jersey okay for another five or maybe even ten degrees lower than normal. I usually getting chilly below 65F, but that base layer will get me down into the high 50’s before I get cold. It’s nice for when a long sleeve base, arm warmers or vest are too much.

  2. That lighter one is certainly a unique feel and very comfy. It doesn’t do much for me below 50 degrees, but the thermal base plus the pro thermal jersey (not to be confused with the pro thermal merino) together make for a very cozy combo that will get close to the freezing point before needing much else. The poly inner and wool outer is a cool activewear idea that I hadn’t seen before and it really seems to *feel* right.

    I should have mentioned I didn’t agree with your comment on sizing up though. I am an inch taller and 20 lbs heavier and I thought all of those in a large fit just like base layers should. Those not wanting a next-to-skin fit should size up though. I just don’t find baselayers to be as effective or layer well when there’s any excess to them.

    Good work. I’m new to the site, but enjoying many of the previous articles.

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