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Castelli Flanders Wool Long Sleeve Base Layer

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Item # CST2705

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Item # CST2705

Who said being sheepish was a bad thing?

Before the advent of synthetic lycras and waffle-weaves, cyclists wore natural fibers such as wool and real chamois leather. And, although you may feel faster wearing all of the latest textiles, for some purposes, wool trumps them all. The Castelli Flanders Wool Long Sleeve Base Layer is a natural alternative to the latest synth craze.

The purpose of a base layer is twofold. First, it provides a comfortable barrier between your skin and outer layers, such as bib tights' straps or rain jackets, and second, it helps to regulate your core temperature. The latter is accomplished by pulling moisture away from the skin so that cold winter air does not create an evaporative cooling effect. Whereas other base layers rely upon combinations of fabrics to wick moisture, the 18 gauge merino wool, from which the Flanders base layer was constructed, does it all.

Merino wool is most known for its non-abrasive qualities, but the benefits don't stop there. Merino wool is what we call a "hydrophilic" fiber, meaning that it has the natural ability to positively interact with water. In fact, Merino is able to absorb as much as 30 percent of its weight before exuding the sensation of wetness. Truthfully, when was the last time you saw a soggy sheep? Because it is able to hold so much moisture, even though the cold air may slow evaporation, your skin will remain dry. When skin is dry, body heat is able to create a small barrier of warm air that acts as an insulating layer.

Additionally, merino wool is naturally antimicrobial. It is a base layer fabric of choice for multi-day adventurers because it does not hold odors. This property is furthered by Merino's natural ability to disperse electrostatic charges, which means your base layer will not pick up lint or dust.

In addition to a form-fit, the Flanders base layer features a high crewneck collar to keep cold from creeping down the front. There are few seams, but when necessary, Castelli uses flat lock stitching to minimize chafing. The back is slightly extended to stay tucked into your bib tights.

The Castelli Flanders Wool Long Sleeve Base Layer is available in sizes Small to XX-Large in the color

Tech Specs

merino wool (18-gauge)
form fit
Claimed Weight:
18 gauge
Recommended Use:
Manufacturer Warranty:
1 year

Size chart


Men's Apparel
 Small Medium Large X-Large 2X-Large 3X-Large
Chest  35.5 - 37in
(90.2 - 94.0cm)
37 - 38.5in
(94.0 - 97.8cm)
39 - 41in
(99.1 - 104.1cm)
41 - 43in
(104.1 - 109.2cm)
43 - 45in
(109.2 - 114.3cm)
45 - 47in
(114.3 - 119.4cm)
Waist 29.5 - 31.5in
(74.9 - 80.0cm)
31 - 33in
(78.7 - 83.8cm)
33 - 35.5in
(83.8 - 90.2cm)
35.5 - 37.5in
(90.2 - 95.3cm)
38.5 - 40.5in
(97.8 - 102.9cm)
41 - 43in
(104.1 - 109.2cm)
Hips 36.5 - 38.5in
(92.7 - 97.8cm)
38 - 40in
(96.5 - 101.6cm)
40 - 42in
(101.6 - 106.7cm)
42 - 44in
(106.7 - 111.8cm)
44 - 46in
(111.8 - 116.8cm)
46 - 48in
(116.8 - 121.9cm)
How to Measure:
For best results, take measurements over your underwear.
Measure under your arms, around the fullest part of your chest.
Measure around your natural waistline, keeping the tape a bit loose.
Measure around the fullest part of your body at the top of your legs.
Using pants that fit well, measure the crotch seam to the bottom of the leg.

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Avg. ride time: 7h 39m per week
  • Average ride time is based on Strava activity over the last 3 months. Give your reviews credibility by connecting your account.

Base layer or cool sweater?

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

Either way, the Flanders Merino wool base layer is awesome. It fits like most Castelli stuff, snug but comfortable. It is relatively thick compared with a lot of synthetic base layers but it also brings the heat. I've taken to wearing mine under my Sanremo Thermosuit for even lower temps. It's proven so effective that I no longer use a jacket at all but simply use the Flanders base layer.

Oh yeah, and it also makes a great casual sweater like top with jeans. On cold evenings in the northwest a Flanders goes a long way toward warm and comfy.

Best Base Layer Ever

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

Soft merino, so nice and warm. Wicks better than poly and doesn't stink. Looks sharp. I bought another one to wear around the house as a light sweater. I wore it skiing at Jackson Hole, worked perfect;y.

I'll take two...

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

This base layer is the favorite piece of gear that I own. Warm, soft, and true to size. I liked it so much that I bought a second...

Oh Yes

    Beautiful, highly-effective, 100% wool baselayer for cold weather. Comes in a box fit for fine jewelry. The wool is very soft. You will be surprised.

    SIZING: The sizing here seems slightly larger than usual for Castelli. I'm 5'10 185. Usually I wear an XL in Castelli (rarely even an XXL). This in an XL is not totally snug around my torso. Maybe they are leaving room for a little wool shrinkage? I will update soon.

    Care: Obviously cold wash either by hand or in a front-load machine. Hang or flat dry. No dryer! And store in zip-lock bag in the off-season (moths).

    Avg. ride time: 7h 32m per week
    • Average ride time is based on Strava activity over the last 3 months. Give your reviews credibility by connecting your account.

    Kept my core warm. Quality product.

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

    This is the first Castelli product that I have purchased and I was very happy with the quality. It did the job of keeping me warm and I was worried about the wool itching my torso but that was not the case.

    Wonderful on and off the bike

    • Familiarity: I've used it several times
    • Fit: Runs large
    • Size Bought: L

    Love this base layer: keeps you warm when needed without trapping heat and overheating when temperatures get warmer.
    I enjoy wearing it off the bike as a comfortable and soft sweater just as much as I like it as a base layer underneath long sleeve jersey and (if needed) jacket.
    I am generally an L with Castelli, and so I ordered this in L also. It seems too baggy, though still usable. If I ever buy another one I will downsize to M (6'2" 190).

    warm and looks good

    • Familiarity: I've used it several times

    I had doubts about how warm this would be when first viewed, but it was soft against my skin {not scratchy] and combined with the Gore Phantom jacket i was comfortable at 32 degrees. This will be a favorite by itself or layered.

    Wooly Bully

    • Familiarity: I've put it through the wringer

    This piece is bossy. 6'1 180lbs... I like an XL for a hugging fit. It handles hot and cold with ease. I throw this underneath a thermal jersey or a jacket on colder days. i always gravitate to this above my other Flanders Warm and WS because of the way it breathes. The synthetics simply sponge and hold too much moisture. The Flanders Wool owns in temps from 30 to 55. Classy and comfortable design. I love this guy.

    Wooly Bully

    Are you wearing that under the Alpha Jacket? If so how do you find the 2 work together?

    Like Peanut Butter & Jelly. They are perfect together. If things get toasty start to work down the ladder. The wool provides a less intense warming that allows you to ride hard in cold temps and not get too wet. For me, the wet/cold is the most uncomfortable. Unzipping the outer of the Alpha allows you to dry the base layer almost instantly. The wicking and drying of this base is truly top notch.


    • Familiarity: I've used it several times

    Warm when it's cold. Cooler as it warms up. Comfortable up to about 60 or 65 degrees. Dries very fast and is still effective if slightly damp from mist, sweat, etc as only wool can be. Very comfortable - wore it all day on a cool double century. Keep them in a Ziploc bag... moths love them too! I own two for now.

    great wool jersey

    • Familiarity: I've used it once or twice and have initial impressions

    I love the feel of well-made wool. This has a great fit and feel! Nicely tailored. I expect to get many years of use from this jersey.

    mine doesn't look like the picture

    • Familiarity: I've used it several times

    my XXL has white stitching all over. not a real big deal, but the pic should be changed to reflect the actual product. also, the logo on the chest is way bigger.