Castelli Seamless Men's Sleeveless Base Layer
CastelliSeamless Men's Sleeveless Base Layer


A seamless base layer makes for one of the hardest working and most versatile pieces in your wardrobe. If you don't have one, start with Castelli's Seamless Men's Sleeveless Base Layer; you'll barely know you have it on under kit, but the whisper-thin nylon and polypropylene fibers will quietly work throughout your ride to shuttle moisture from your skin to your jersey, keeping you cool and dry on warm days. Keep it in your rotation when the temperatures start to drop and it will begin to act as an insulating layer during chilly mornings and windy descents. Castelli constructs the base layer expertly, as usual, to mimic your body movements in the saddle and remain next to your skin to wick moisture as quickly as possible. It weaves the synthetic fibers in an open mesh pattern to ensure air moves freely throughout the base layer, adapting to changing ride conditions without inhibiting your movement in the saddle.

  • Destined to be one of the most versatile additions to kit
  • Insulates in the cold, wicks moisture in the heat
  • Contoured, seamless cut to move with you in the saddle
  • Reviews
  • Q & A

Still very good

  • Familiarity: I've put it through the wringer

Its my second pair, I still have the one that I bought in 2015. The new one is great and bright white. The fit follow the Castelli chart.
PS - The older one never be stink as other baselayers.

I wear a Large in a Gabba 2 Jersey- 5-7, 169 LBS.
Bigger in the chest/shoulders, waist-33.
Thinking L/XL??

I would agree the L/XL, I wear the same size in the castelli base as I do the jersey.


  • Familiarity: I've used it several times
  • Fit: True to size
  • Size Bought: L/XL

Miraculously warm. On a three-hour, 55° ride, I had to unzip the jersey I had as my outer layer--even during fast, long descents. I felt like as if I could have done away with an outer layer altogether. The fit is tight, but I think it's supposed to, in order to work its magic. Looks and feels as if you're wearing a stretchy string bag. I'm careful taking it off and putting it on, since it seems as if it might stretch too much or even rip. No problems yet. An essential piece of cold weather kit.

Makes a Difference!

  • Familiarity: I've used it several times
  • Fit: True to size

Worn under bike jersey this provides a neat layer of moisture wicking resulting in a cooler and more comfortable ride. It also helps to hold the heart rate monitor in place. Snug, but not terribly so. I'm 32-34 waist and 41-42 chest and L/XL fit well.


  • Familiarity: I've put it through the wringer
  • Fit: Runs small

This 'open mesh' vest baselayer is designed to keep you cool in warm weather by holding your jersey *off* your skin. In addition, the special (hollow-fiber) textile pulls sweat off your body and evaporates it away.

Anyway, it works. Wear this vest baselayer under your favorite summer jersey, and you will run cooler.

Paradoxically, in cold weather... worn under a long-sleeve baselayer and a jacket... this vest creates a kind of insulation zone, and promotes sweat evaporation, and reduces claminess.

Very comfy! Zero seams. Not one. Very clever/sophisticated Italian sock machine manufacture.

Sizing: As Castelli vets know from experience... size up +1 from your normal street size. I wear a street L and the L/XL here fit perfect. Snug and wrap around, as a baselayer should be.

This vest runs a bit long (a bit annoying) so tuck over in your shorts if necessary​. The size L/XL, in length, will certainly fit tall riders. Up to 6'2", I would think.

Unique and Awesome

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

Interestingly enough, this works really well even when it's a bit colder outside. One of the most unique garments I own because of this, and it stretches more than you'll think it will. It makes it a bit difficult to get off, but works really well as a hot weather base layer. Even though it is a very open mesh pattern, the thickness of the material keeps a pretty solid distance between your skin and the jersey you wear on top, creating a lot of potential airflow to keep you cool. Combine this with a good, breathable jersey and you're good to go in just about any level of heat.

fits tights and feels great

  • Familiarity: I've used it several times
  • Fit: True to size
  • Size Bought: L/XL

This is what an undergarment should be: comfortable, provides breathing space and tight enough not to bunch up under the rest of the kit. Due to the tight fit, if you've got shoulder issues, you may need help getting it off. I find it wonderful.

Work great!

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

I got this base layer for the summer rides and it performs great. What i discovered is that it works even when the temperature goes down. I have used it with my long sleeve jersey and a vest in the low 40's. I found that i am actually warmer with the base layer than without. Reason, my thinking is that i am putting space (air is a wonderful insulator) between my body and jersey.
Works great in the summer too, but that is what it is for.

My favorite base layer!

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

I absolutely love this product. It is my go-to base layer, so much so I feel naked without it. I'm hoping santa brings me a few more for Christmas this year. It runs true to size, you definitely want it to fit snugly in order to function properly. Once you wear it, you'll never want to ride without it.

Very cool

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

Very confortable, it didnt stink as other baselayers

Very cool

I'm right between the medium and large; what size should I order? I normally wear medium jerseys, but the occasional large for euro brands. The small being paired with the medium has me worried!

Best Answer

I typically wear M jerseys as well. I'm 6' 160lbs and the S/M fits great. The mesh material can stretch a lot and the length is good.

Great base layer

  • Familiarity: I've used it several times

Castelli's Seamless base layer is great! I am 5'8 - 5'9 165lbs and I have a stocky short torso.

The base layer is very true to size for Castelli's line of cycling gear. It sits well around the neck, sleeves and hip area. Its snug enough to wear over my jerseys without discomfort.
The material is fairly thicker than the base layers I am familiar with but even in summer Southern Californias Summer weather the layer does it jobs with ease.
It feels very sturdy even through all the washes it has endured so I am very pleased.

Sorry for the late reply. I bought a Medium sized base layer!

??? ??????.

    이번에 카스텔리에서 Sleeveless Base Layer를 구입했는데, 착용감이 너무 좋아 벌써 부터 여름이 기다려집니다.

    절대 강력 추천하는 품목입니다. ^^

    Yes I agree completely

    Does this base layer provide sun protection?...

    Does this base layer provide sun protection? i.e. can I use it under the Climbing jersey and not worry about getting a sunburn?

    Hi Perry,

    The Castelli Seamless Men's Sleeveless Base Layer would not provide adequate sun protection.

    It has a very open mesh weave that would expose the skin to the sun.

    Must have in summer

    • Familiarity: I've put it through the wringer

    This base layer is like having air conditioning in the summer! It creates space between your body and your jersey to allow air to flow in between and cool your skin. It also pulls the sweat off your body. Makes a big difference when riding in 90-100 degree temps. I am 6'3", 195 lbs and went with the L/XL as the piece stretches and you want it to fit tight.

    B7, which is better? Castelli's "seamless" baselayer above... or Castelli's "core mesh" vest baselayer? They seem almost identical.

    According to CC, the seamless has different mesh patterns to breath better in key areas.

    I own both the seamless and core mesh and prefer the seamless on hot days. The seamless is thicker, but that allows more air to pass through between your jersey and your skin. The core mesh still does it's job, but the seamless is a few notches above.

    A better view of the baselayer

    As you can see from the open mesh, it's nothing like a t-shirt baselayer. Looks pro with a jersey, though.

    A better view of the baselayer

    This baselayer won't overheat you

      I never would have thought that a baselayer would be a good thing to have, but a crash where I got road rash on my back showed me otherwise. An extra layer might have spared me a week of road rash healing.

      But...a baselayer for hot weather? Crazy! But not really. The mesh construction lets air flow freely, helping keep me cool. Most telling, my torso feels reasonably dry during the ride but when I take the jersey off it's soaked. So the baselayer transfers sweat outward.

      The material's stretchy, so as small as these are they're more forgiving than they look. But don't wear these minus the jersey unless you want weird looks.