Isadore Merino Long-Sleeve Baselayer review – more versatile than just a base

There’s no magic to it, but this midweight merino top hits the spot nicely as a relaxed spring all-rounder as well as a cold-weather base

Man in black long-sleeved base layer
(Image: © Sean Fishpool)

BikePerfect Verdict

With the usual pros and cons of merino wool, this is bike clothing without feeling too much like bike clothing, and its weight and cut give it a nice versatility.


  • +

    Comfort against the skin

  • +

    Warmth, even when damp

  • +

    Versatile middleweight fabric

  • +

    Can be worn snug or relaxed


  • -

    Holds damp, like all merino

  • -

    Isadore’s wool is mostly mulesing-free but not 100%

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I’ve been testing a boxful of base layers this winter. They’re nearly all pretty good, in cut, or the performance of the fabric, or whatever. But a particular few I keep coming back to more than the others, and the Isadore Merino Long Sleeve Baselayer is one of them.

Even though we’re out of the frosty season as I write this, its weight and density mean that as well as having served as a decent under-layer in colder weather, it’s nice to ride in as a luxurious long-sleeved tee by itself on milder days, so it’s still providing great service into May.

I haven’t spent a huge amount of time in merino tops in the past, despite being a fan of the way wool cycling socks stay warm when wet, mainly because I’ve been so pleased with the dryness and warmth of synthetic thermals. And while I wouldn’t yet say that I’m a complete convert to the ‘damp but warm’ way of merino, I do like the very pleasant yet performant way that this particular top feels like ‘clothes you can cycle in’ rather than ‘cycling clothes’.

Man in black long-sleeved base layer

We’re wearing a more relaxed size; you can size down more snugly too (Image credit: Sean Fishpool)

Design and specifications

Some of the merino winter base layers I’ve been testing are thin and light, giving you merino’s soft feel against the skin and making for easy layering, while capitalizing on the way that merino punches above its weight for warmth. The Castelli Bandito long-sleeve tips the scales at 123g, for instance. But the Isadore Merino Long-Sleeve Base weighs in at 243g, not far off the weight of an equivalent brushed fleece winter jersey.

The 100 percent merino fabric has merino’s usual soft, low-odor, low-scratch qualities, and it’s got enough stretch that you could easily choose a snug-fitting size, while not keeping a fitted shape if you opt for a looser fit. Refreshingly for a base layer, it comes in some pleasingly nature-inspired colors (fig, avocado, and um, string) as well as conventional base layer black.

Isadore itself places an emphasis on ethical and sustainable production; with manufacture in their home country of Slovakia and a number of environmentally focused projects including jersey rental and synthetic garments made from recycled materials. One thing you should be aware of when looking at merino is the controversial farming practice of mulesing, which removes skin around the sheep’s tail to reduce the risk of infection but causes pain and suffering to the sheep.  Most, but not all, of Isadore’s wool comes from non-mulesing farmers – good, but not perfect.

Man in black long-sleeved base layer

The seams are comfortable around the shoulders and underarms (Image credit: Sean Fishpool)


In winter, from temperatures of about 6C / 43F down to freezing, I enjoyed the Merino Long-Sleeve Baselayer under insulated shells like the Castelli Unlimited Puffy Jacket. Those shells can be fine with the thinnest of base layers underneath, but the reassurance of the extra warmth was welcome, especially when you stop and begin to lose heat. 

In spring, as temperatures got over double figures, it was a nice top to start the day in under a light shell, knowing that it would be comfortable by itself as the day got warmer. The weave is dense enough to hold some warmth against moving air, though not colossally so; I’d describe it as a  relatively airy, breathable experience

As every merino user reports, it did get damper than the synthetic alternatives, though mostly you only notice that if you look for it, since it does stay warm. And I’m pleased to report that it did indeed stay fresh smelling over multiple outings without a wash.

I suspect that some of the reason Isadore’s long-sleeve base felt so appealing as an all-round shirt is that I was wearing it a good size up from what I could have done. (The size charts and model photos and sizing widget are a bit inconsistent; the charts say a 36in chest is a medium; the model photos say that someone 20cm taller and 20kg heavier is also a small; the sizing widget says that I’m an XS…). I think all that means is that if you want a traditional snug base base, go with the sizing widget and it will serve that purpose nicely; if you want  close but relaxed, go a size or two up.


There’s nothing super-miraculous about the Isadore Merino Long-Sleeve Base; pure merino is pure merino. It’s just a nicely made, nicely cut top in a satisfyingly versatile weight… at a moderately premium price. 

Tech specs: Isadore Merino Long-Sleeve Baselayer

  • Price: $90/ £70 / €75
  • Weight: 243g (M)
  • Sizes: Men’s XS-XXL; Women’s XXS-XL
  • Colors: Fig, avocado, string, black (tested)
  • Key  materials: 100% merino wool
Sean Fishpool
Freelance writer

Sean has old school cycle touring in his blood, with a coast to coast USA ride and a number of month-long European tours in his very relaxed palmares. Also an enthusiastic midpack club cyclocross and XC racer, he loves his role as a junior cycle coach on the Kent/Sussex borders, and likes to squeeze in a one-day unsupported 100-miler on the South Downs Way at least once a year. Triathlon and adventure racing fit into his meandering cycling past, as does clattering around the Peak District on a rigid Stumpjumper back in the day.

Height: 173cm

Weight: 65kg

Rides: Specialized Chisel Comp; Canyon Inflite CF SLX; Canyon Aeroad; Roberts custom road bike