Ski base layer bottoms, ranked by the gram weight on the label

Why gram weight is the only number that matters

Base layers are sold on adjectives - thermal, midweight, performance - and almost none of that is comparable. A gram weight is: g/m2 is the mass of a square meter of the fabric, so a 320 is roughly twice the fabric of a 165, and two garments with the same figure are genuinely comparable regardless of brand.

It is the same axis our base layer roundup ranks tops on, and the reason that page exists in the shape it does. This page is the bottom half of the same wardrobe, and it was missing: the tops roundup carries four crew-neck tops and no bottoms at all.

Who each of these is for, and who should skip it

• Most people, most days: the 165 g/m2. Cheapest here, lightest published weight, and the one that will not make you sweat on a moving day.
• Cold days, or matching a 250 top: the Smartwool Merino 250. The same published weight as the Smartwool top this site already ranks, so the pair is directly comparable.
• Standing still in real cold: the 320 g/m2. It carries the skip note because that is a narrower case than people think.
• Skip bottoms entirely if you run hot and ski spring. Insulated ski pants over bare legs is a legitimate choice in April - what to change for spring.
• Skip all of these for a child and buy the kids' weight instead. The kids' base layer roundup - and it points out the half everyone forgets.

What this page ranks on

• 1. Published gram weight. The entry requirement. A bottom that does not state one cannot be compared with one that does, so it is not on this page.
• 2. Published fiber content. 100% merino, a blend, or synthetic. Merino keeps insulating when damp and resists odor; synthetic dries faster and wears longer; cotton does neither and is the one genuine mistake.
• 3. Full length to the ankle. A three-quarter bottom leaves a gap at the boot cuff, which is exactly where a ski boot presses cold plastic against a shin.
• 4. What is published beyond that - which is very little. None of these states an inseam, a warranty term or a US MSRP we could read. Two of the three are Amazon-native brands with no spec page of their own. That is the honest state of this category below the Smartwool price point.

The three, compared

The interesting row is the second-to-last. The dearest item here is the one from the brand with a real reputation, and it is the only one whose weight you can match against a top this site already ranks - but none of the three publishes a reachable spec page, a warranty or an inseam. You are paying the Smartwool premium for the brand and the matched weight, not for more published information.

The picks

100% Merino Wool Base Layer Bottoms, 165 g/m2

The pick, and the one most people should actually buy. Published as 100% merino at 165 g/m2 - the lightest comparable weight here - in a full-length bottom, from the same line that also publishes a 320.

The case for buying light is the one thing this category gets backwards. You are wearing an insulated or shell ski pant over the top, and you are moving: the base layer is not the garment keeping you warm, it is the garment keeping you dry. A heavy base layer under a ski pant makes you sweat on the first climb to the lift queue, and then that moisture is what makes you cold sitting on the chair. Light merino moves it out; heavy merino holds it.

At this price it is also the practical answer to the actual problem most first-timers have, which is skiing in cotton leggings or jeans - what not to wear skiing, and what to wear instead. Getting somebody out of cotton matters far more than which merino weight they land on.

Honest cons. Too light on its own for a genuinely cold day without a real mid layer above. An Amazon-native brand with no reachable spec page, no warranty term and no MSRP. Light merino wears through at the heel and seat faster than heavier weights or a synthetic blend. And no inseam or fit detail is published.

Smartwool Merino 250 Base Layer Bottoms

The cold-day pick, and the only one here from a brand this site already ranks on the top half. Published as Merino 250 - the same 250 g/m2 figure our base layer roundup uses to compare fabrics - in a full-length bottom.

The genuine argument for it, beyond the badge: a matched set. If you own the Smartwool Classic Thermal Merino crew that the tops roundup ranks, a 250 bottom gives you a layer whose behavior you already know rather than a guess. That is worth something on a trip where you cannot try things.

It is also, by a wide margin, the most expensive item on this page - several times the 165. Smartwool publishes the weight and essentially nothing else we could read: no inseam, no warranty term, no MSRP.

Honest cons. The price, which is the main one. 250 g/m2 is too warm for spring and for anyone who runs hot. Merino wears through at the heel and the seat sooner than a synthetic blend, which stings more at this price. And no fit information is published at all.

100% Merino Wool Base Layer Bottoms, 320 g/m2, and why it carries the skip

The warmest published weight here, and roughly half the Smartwool price. Published as 100% merino at 320 g/m2, from the same line as the 165 - which is what makes the pair internally comparable and is the reason both are on the page.

It carries the skip because 320 is more layer than a skiing day wants. A skier generates heat; the person who needs 320 g/m2 against the skin is the one standing still - watching a lesson from the bottom of the slope, running a lift, or skiing somewhere reliably below 10F. How cold is too cold to ski is the page for that end of the range, and the temperature table puts this weight where it belongs.

Honest cons. Too warm for most resort days and far too warm for spring. Bulky under a fitted ski pant, which affects how the pant sits over the boot. Slow to dry overnight, which matters on a multi-day trip. And the same missing information as the 165: no spec page, no warranty, no MSRP, no inseam.

What else goes under a ski pant

A base layer bottom is one of three things down there, and the other two matter more than people expect.

• One pair of ski socks, thin, over the base layer not under it. The sock goes outside the long underwear so there is no seam ridge inside the boot cuff - and the thin pair is the warm one.
• Nothing cotton, anywhere. Not the base layer, not the socks, not the underwear. What to wear under ski pants, and what to leave at home is the guide this page is the commercial half of.
• No second layer unless it is genuinely bitter. Two bottoms inside a fitted ski pant compresses the air that does the insulating and restricts circulation - the same mistake as two pairs of socks.
• And the pant itself does most of the work. Why ski pants matter more than the jacket, and whether a bib closes a gap you actually have.

Making merino last

• Wash it far less than you think. Merino resists odor; washing is what wears it out. Air it overnight and wear it again.
• Cool wash, no fabric softener, no bleach. Softener coats the fiber and kills the wicking - the washing page covers the whole kit.
• Dry flat, not on heat. Heat shrinks and felts wool, and a shrunk base layer is a dead base layer.
• Expect the heel and seat to go first. Those are the abrasion points inside a boot and against a chairlift.
• Store it clean and dry over summer. Moths find merino, which is the one storage risk a synthetic does not have - the end-of-season routine.