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Lightest Wool T-Shirt: Black Diamond Rhythm Tee Review

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Last spring, Black Diamond debuted a merino wool shirt that’s among the lightest ever made. GearJunkie wanted to investigate how well the outdoor layer holds up over time. Our conclusion? Surprisingly well.

Black Diamond’s Rhythm Tee is an ultra-lightweight top that weighs less than most technical wool shirts. This crew-neck short-sleeve is a wool-nylon blend called Nuyarn. The textile is constructed by weaving merino wool around a nylon core. The layer is stretchy, thin, and built to dry faster than similar wool-synthetic blends.

This fabric technology is not entirely new but is growing in popularity. Trew Gear debuted the Weightless Nuyarn Merino T ($65; men’s and women’s) and men’s Superlight Nuyarn Merino Pocket T ($69).

And Black Diamond expanded its Nuyarn lineup. Now, the Solution 150 Merino Base Crew long-sleeve ($119) is available for men and women. And the Solution Merino Hoody ($229) is offered for men.


In short: The Rhythm Tee is very light and dries fast but is expensive. The price is $75, which matches the bill of comparable high-end outdoor tees in the same category. Our other favorite women’s active T-shirts cost an average of $55.

The good news is that the Rhythm Tee is durable and lasts over time, which makes the extra cost worthwhile. Read on to learn more.

Note: The following gear review covers the women’s Rhythm Tee, but the men’s version has the same composition and weight.

Black Diamond Rhythm Tee Review

I wore the Rhythm Tee for trail runs, hikes, dirt biking, mountain biking, and rock climbing during summer and fall 2019. I also trained for and completed the Sage Burner 50K using this shirt. The ultradistance trail-running event takes place on rolling, high-desert terrain in the fall.

Warm days in the shirt ranged from 70 to 85 degrees Fahrenheit with clouds, direct sunlight, and occasional wind chill. In October, temperatures dropped to include below-freezing and frosty mornings as well as chilly afternoons.

Then, I tested the T-shirt as a base layer for backcountry touring in the winter. Temperatures ranged from 10 to 30 degrees F. I typically get colder doing lift-served skiing or snowboarding, so I wear a long-sleeve base layer at ski areas.

The Rhythm Tee was also a great everyday shirt beyond outdoor activities. I pulled it on for around-town errands, housework, moving, indoor workout classes, and property maintenance like snow shoveling.

Superlight T-Shirt

The Rhythm Tee is among the lightest technical wool shirts on the market, as verified throughout testing. First, the Rhythm Tee felt ultralight compared to other performance T-shirts that I regularly use.

The fabric is even slightly transparent. When I hold the shirt up to ambient light, I can see clearly through the layer. However, in my experience, the shirt is not airy enough for the skin to be visible.


The T-shirt is labeled as 69 g. My Rhythm Tee is a size medium and weighed a bit more (71.7 g) according to my scale. I weighed other performance T-shirts from my closet, and they were heavier than the Rhythm Tee. My Tasc Performance cotton-bamboo shirt was 100 g. And an Under Armour polyester-elastane blend was 83.91 g.

The Rhythm Tee is light because Nuyarn wool-nylon is 95 g per square meter (gsm). Several other popular wool-blend performance tees use core-spun yarns, where merino wool is twisted around nylon. In general, ultra-lightweight core-spun wool blends are closer to 150 gsm. The icebreaker Tech Lite Short Sleeve ($75; women’s and men’s) is core-spun and 150 gsm.

The Smartwool Merino 150 Base Layer Short Sleeve ($75; women’s and men’s) is also core-spun and 102 g.

Durable Wool T-Shirt

My greatest concern with the weight of the Rhythm Tee is that it would not be durable over time. Merino wool strands typically have diameters between 15 and 23 microns. Wool is finer and softer when it has a lower micron measurement.

This shirt’s merino wool is 18.5 microns. But this T-shirt is 43% merino wool and 57% nylon, which reinforces the merino wool.

To my surprise, the shirt withstood recreation and everyday use really well. The Rhythm Tee’s stretch and elasticity have remained constant throughout testing. In the past 8 months, I’ve worn this shirt nearly once a week. The fabric has been brushed against then washed and thrown into the dryer more than 30 times. There are no tears, visible stains, or undone seams.

However, the fabric does show slight pilling. And the seams are wearing down a bit where pack straps sit.

Fast-Drying & Odor-Free

The Rhythm Tee dried really fast during and after activity. Generally, I sweat a lot throughout outdoor cardio or gym conditioning. I’m relieved when a shirt can dry during a 10-minute break.

This quick-drying fabric prevented me from getting chilled on short trail runs and longer 5- to 7-hour runs. And the tee’s fast-drying nature was favorable after exercise classes during the walk home.


This shirt was also great to pair with packs during mountain biking, hiking, and ultrarunning. I always perspire beneath a pack’s straps and back panel. But when I’d remove my ultrarunning pack at aid stations during the Sage Burner 50K, the Rhythm Tee would dry in about 5 minutes.

One of my favorite qualities about the Rhythm Tee is that it prevents odors extremely well. I wore this shirt all day while moving, including wrestling heavy boxes and furniture, shoveling snow, and handling stressful situations. To my surprise, the shirt did not smell bad that night.

The shirt also did not stink after the Sage Burner 50K. The Rhythm Tee’s natural odor prevention made it a stellar choice for travel days or trips when I needed to handwash my clothes.

The Bottom Line

Nuyarn-based shirts like the Rhythm Tee are not the only well-made wool-synthetic option. However, this shirt’s dry time and lightweight character are exceptional. The shirt is very durable, especially for its density. And it covers stench like a charm.

Furthermore, the fit is attractive: a tad longer, slightly tapered, and non-form-fitting. The shirt’s style and silhouette make it appeasable for casual use too.

_DSC9678_PC Eric Phillips

My greatest critique is that the Rhythm Tee isn’t super soft. If you have hypersensitive skin, the Rhythm Tee might feel slightly abrasive. For instance, the material was noticeable when I would pull on a midlayer during fall and winter season activities. But after a few minutes, I would adjust and not notice the fabric anymore.

By comparison, the Le Bent Le Base 200 Lightweight Crew long-sleeve is the softest performance shirt I’ve tested to date. The Le Base fabric is primarily rayon from bamboo (66.5%) and 28.5% merino wool.

Another shirt that’s softer than the Rhythm Tee is Janji Swift Tech Merino LS Mock-Neck long-sleeve. The Swift Tech is 84% polyester and 11% merino wool.

However, the overall benefits of the Rhythm Tee keep this shirt on my go-to list. The price is a reasonable investment because the shirt lasts. If you’re looking for a performance tee that’s durable for outdoor adventure and looks good for casual days, the Rhythm Tee is a competitive option.

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