Running Inner Layers: Start with a 46g LayerDrylayers, base layers and inner shorts compared by official weight

If you are buying 1 running inner layer first, it is finetrack's Drylayer Basic T (46g). A non-absorbing undergarment with an absorbing shirt layered on top, so it does not depend on season. The layer closest to the skin ranges from 46g to 110g by official weight. The Cool T, which the same company explains as "the thinnest," is 72g, so the thinner one is 26g heavier. For inner layers, thinness and lightness do not line up in the same direction.

The "thinnest" drylayer is 26g heavier

finetrack has 2 pieces of the same shape for running drylayers: the Drylayer Basic T at 46g and the Drylayer Cool T at 72g. The Cool is the thinnest in the series, a piece whose fabric is about 20% thinner than the Basic.

The thinner one is 26g heavier (72 − 46). The reason is in the material field. The Basic is 100% polyester; the Cool is 88% nylon and 12% polyurethane. The thread changed, and with 12% stretch thread added, the weight went up.

What the Cool buys is not lightness but coolness. The value q-max, which shows coolness to the touch, is 0.258 for the Cool and 0.115 for the Basic. About 2.2 times (0.258 ÷ 0.115). Line up inner layers by weight alone and this difference disappears.

The order of running layers: skin, non-absorbing underwear, absorbing shirt, shell

finetrack divides layering from the skin side into 5 layers, L1 to L5. L1 is the drylayer, L2 the base layer, L3 the insulating mid layer, L4 a thin shell that stops wind, and L5 the outer shell against rain and snow.

What readers rarely know, I think, is how L1 works. The drylayer is a mesh with a water-repellent finish and does not absorb sweat. L1's water repellency keeps sweat off the skin, and the L2 base layer absorbs that sweat. It is a thinking that splits the absorbing job and the skin-touching job across 2 pieces.

So a drylayer is not something to wear alone. The product page also carries a note that it shows its effect layered with moisture-wicking, quick-drying wear. Water repellency is a finish that wears off with washing; in the company's own test, how much water repellency remains after washing is 80 points at 150 washes for the Basic and 80 points at 100 washes for the Cool.

Millet's Drynamic Mesh is an undergarment worn in the same place but works differently. The material is 66% polypropylene, 28% nylon and 6% polyurethane. A bulky mesh sends sweat on the skin to the base layer above, and the mesh thickness keeps the wet base layer away from the skin.

finetrack is a "thin water-repellent film," Millet a "thick net." Even in the same L1, the 46g versus 100g gap is this difference in build. Most running days end with 2 layers, L1 and L2, or 3 with a wind-stopping piece added.

How to choose running inner layers: the conditions I used

I lined up 12 current men's pieces. Materials and prices are the Japan official site listing of Oct 13, 2026. Where weight is written officially, I sorted lightest first.

The 3 companies that wrote weight on the product page were finetrack, Millet and mont-bell. Under Armour, Icebreaker and C3fit I compare by material share and price.

Drylayers that keep sweat off the skin: 46g, 72g, 100g

Scroll the table sideways →

No. 1: Drylayer Basic T. The lightest of the 3 at 46g. A good balance of warmth and sweat release, not dependent on season. If you buy it as a first piece, this is the one you use all year round. Two things to watch: at about JPY 121 per gram it is the highest of the 3, and the fabric is "delicate," with notes to avoid hook-and-loop fasteners, snagging on branches and dryers.

No. 2: Drylayer Cool T. As at the top, an undergarment about 20% thinner than the Basic and 26g heavier. It suits hot seasons and sweaty exercise. The sleeveless version is 62g, a 10g gap from the T (72 − 62). What to watch is that its warmth is about half the Basic's (finetrack's comparison), so it is not a piece for winter mornings. The price is JPY 1,441 more than the Basic (6,985 − 5,544).

No. 3: Millet Drynamic Mesh NS Crew. 100g, about 2.2 times the weight of the Basic T (100 ÷ 46). It is heavy because the net itself has thickness. That thickness does the work of keeping the wet base layer off the skin. Price per gram is about JPY 58, the lowest of the 3. What to watch is that it is sleeveless at 100g. The short-sleeve version with sleeves is 110g and JPY 6,600.

By lightness, the Basic; by heat, the Cool; to keep wet clothes off the skin, the Millet.

Summer base layer: a 67g mesh, or a stretchy single piece

No. 1: mont-bell Geoline Cool Mesh T-shirt. 67g and JPY 2,860. Price per gram is about JPY 43 (2,860 ÷ 67), about a third of the Drylayer Basic T. Fine bumps on the fabric surface reduce the area touching the skin, so you feel less stickiness. This is an undergarment on the absorb-and-dry side, a different role from the water-repellent L1. What to watch is that, being ultra-thin mesh, it shows through as clothing to run outside in on its own. The sleeveless version is 56g and JPY 2,640.

No. 2: Under Armour HeatGear Armour. A single piece worn tight to the body, with 16% polyurethane. Its features are moisture-wicking quick-dry that sends sweat outward, a 4-way stretch fabric and mesh panels. It is built so you can appear in public in it alone. What to watch is that the body line shows as it is. If you want to wear something loose, there are other ways to choose.

To wear under a running shirt, mont-bell; to wear alone, Under Armour.

Winter base layer: 120g synthetic versus about 128g merino wool

Scroll the table sideways →

No. 1: Geoline L.W. Round Neck Shirt. 120g and JPY 3,740. Light and fast-drying, suited to exercise where you sweat hard in cold seasons. For a runner's winter piece, this first. At about JPY 31 per gram, it is the lowest of the 12 in this article. What to watch is that being thin, on days with long stopped time you need 1 more layer over it. The short-sleeve T-shirt is 96g and JPY 3,080, a 24g gap from the long sleeve (120 − 96).

No. 2: Super Merino Wool L.W. 85% wool at about 128g. The weight gap from the synthetic is only 8g (128 − 120). The price is JPY 3,850 higher, about 2 times (7,590 ÷ 3,740). A material with high warmth and good stretch even when thin. A piece for days when you spend more time walking and waiting than running and sweating.

No. 3: Icebreaker 200 Merino Oasis. Mid-weight, 100% merino wool. It claims to be less itchy even directly on the skin. The price is about 2.4 times mont-bell's merino (17,930 ÷ 7,590). It is sold in overseas sizing, about 1 size larger than Japanese sizes. If you want to compare weight in numbers, choose from the 2 above.

Synthetic on running days, wool on days with long stopped time. It is not decided by the 8g gap but by speed of drying and price.

Inner shorts and short tights: 34g, 36g, 70g

Running shorts come with an inner or without. What to wear under the mont-bell Cross Runner Shorts Light (98g) that I placed at No. 1 in the article on running apparel is decided here too.

No. 1: Drylayer Basic Boxer. The lightest of the 4 at 34g. The crotch has a backing that absorbs sweat. What to watch is that at about JPY 143 per gram (4,851 ÷ 34) it is the highest in this article. Like the T above, it is an undergarment meant to have an absorbing fabric layered over it.

No. 2: Geoline Cool Mesh Trunks. 36g, a 2g gap from No. 1. The price is under half (2,310 ÷ 4,851 = 0.48). This is a fabric on the absorb-and-dry side, with airflow and fast drying as its features. If you try just 1 piece first, this is the easiest to start with. It has no stretch thread, so for people who want a body-hugging shape, the Geoline L.W. Fit Trunks (50g, JPY 2,800) with 3% polyurethane are the way.

No. 3: Drynamic Mesh Boxer. 70g, about 2 times No. 1 (70 ÷ 34). Even if the shorts above get wet, the mesh makes a gap between the wet clothes and the skin. An undergarment for rainy days and mountain paths that cross streams. For a sunny road 10km, it is 1 piece that is just 36g more.

No. 4: C3fit Compression Half Tights. Tights up to above the knee with 26% polyurethane. They claim to limit extra wobble of joints and muscles through a compression design. That is the maker's explanation, and in this article I line up only material and price. The price is about 5.2 times mont-bell's trunks (12,100 ÷ 2,310).

This is a purchase that changes the shape of the shorts themselves. People who choose lightness by numbers decide from the 3 above.

The pick for each scene, and the total of the layers

I apply the numbers so far to 4 scenes. For the shirt worn on top, I calculated with the same mont-bell Cool Light T as in the running apparel article (80g, JPY 4,000), the EX Light Wind Jacket (45g, JPY 9,680) for the wind shell, and the Versalite Jacket (143g, JPY 24,000) for the rain jacket.

Scroll the table sideways →

Summer full marathon: Drylayer Cool T. finetrack lists the Cool and an ultra-thin base layer for warm-season running combinations. The full is an event where you run for 3 to 6 hours in a shirt soaked with sweat. With the Basic T the total would be 126g, 26g lighter (46 + 80), but I take the one with about 2.2 times the q-max. For races up to 10km, a single shirt is enough without adding an undergarment.

Winter training: Geoline L.W. Round Neck. A synthetic long sleeve billed for "hard-sweating exercise in cold seasons." Layer a 45g wind shell over it for 165g. On windless days, take off the shell and run at 120g. Adding the 46g Basic T underneath gives 211g, the 3-layer form finetrack recommends for cold-season trail running (46 + 120 + 45).

Trail, rain: Drynamic Mesh NS Crew. On rainy days, a shirt gets wet not only from sweat but from water from outside. This is the scene where Millet's explanation of keeping a wet shirt off the skin by thickness applies as it is. Of the 323g for the 3 layers, the rain jacket takes about 44% (143 ÷ 323).

HYROX (indoor): HeatGear Armour. Indoors there is no wind or rain, and nothing to layer over. With little point in splitting the absorbing job and the skin-touching job across 2 pieces, choose one made to be worn alone, that stretches along the body. The clothes for the venue as a whole are lined up in the article on HYROX apparel.

Add underwear top and bottom and 218g becomes 298g

In the running apparel article, I calculated 3 pieces, sleeveless 63g, shorts 98g and socks 57g, at 218g and JPY 12,700. Add the drylayer top and bottom to that.

Basic T 46g + Basic Boxer 34g is 80g. The total is 298g (218 + 80). The price rises JPY 10,395 (5,544 + 4,851) to JPY 23,095.

The weight is about 1.4 times (298 ÷ 218) and the price about 1.8 times (23,095 ÷ 12,700). You pay almost the same amount for 2 undergarments as for the 3 pieces of clothing. If you swap only the bottom for mont-bell's Cool Mesh Trunks, the added cost drops to JPY 7,854 (5,544 + 2,310).

Who is it for?

A drylayer works on days you wear a wet shirt for a long time. On a cool road up to 1 hour, a single moisture-wicking, quick-drying shirt dries the sweat as it is.

Merino wool is a piece for people who reuse it for mountaineering and camping too. For winter running alone, synthetic costs less. The gap is 8g and the price about 2 times.

If your shorts have an inner, you can run as you are. Layering 2 adds seams.

FAQ

Can I wear a drylayer by itself?

It is built to be layered. The effect appears when layered with moisture-wicking, quick-drying wear. The fabric does not absorb sweat, so with nothing above to absorb it, the sweat has nowhere to go. To wear 1 piece alone, use a garment on the absorb-and-dry side, such as mont-bell's Cool Light T or Under Armour's HeatGear.

Which should I buy first, the finetrack or the Millet drylayer?

For road runners, the finetrack Basic T. At 46g it is under half the Millet (46 ÷ 100). For people who run rainy mountains or carry a pack, the Millet. The mesh thickness keeps wet clothes off the skin. The price gap is JPY 286 (5,830 − 5,544), nearly the same.

For winter running inner layers, merino or synthetic?

On running days, synthetic. mont-bell's synthetic is 120g and JPY 3,740; the 85% merino wool is about 128g and JPY 7,590, an 8g weight gap and about 2 times the price. Send the wool out on days when you walk or wait long. For the windbreak you layer over it, the article on running outer layers compares weight and water resistance.

Why are Patagonia, Mizuno and Wacoal CW-X not in the table?

Because on Oct 13, 2026, the day I checked, the Japan official sites of Patagonia and Mizuno showed maintenance. For the CW-X sports shorts, the official store's stock field showed "not handled," so I could not tell whether they are sold now.

Gear in this article

Ads and images: Rakuten Ichiba

finetrack Drylayer Basic Tfinetrack Drylayer Cool TMillet Drynamic Meshmont-bell Geoline Cool Meshmont-bell Geoline L.W. Round Neck Shirtmont-bell Super Merino Wool L.W.C3fit Compression Half TightsUnder Armour HeatGear Armour Compression Short Sleeve

Related reading

A Full Running Kit (Top, Bottoms, Socks) for 218gRUN GEAR NOTECompared by official specs2026.10.15Product image: Rakuten IchibaPictured (Rakuten Ichiba): mont-bell EX Light Wind Jacket / mont-bell Cool Light T / Sleeveless Shirt / On Performance-T / mont-bell Cross Runner Shorts LightA Full Running Kit (Top, Bottoms, Socks) for 218gShirts, pants, socks and jackets compared by official weight. A full running kit of top, bottoms and socks comes to 218g and JPY 12,700. The first thing to add is mont-bell's 45g wind shell. I compare mont-bell, Nike, On, Tabio and The North Face by weight, fabric and price from their official Japan sites, and say exactly what to wear for each temperature and distance.Shoes & gear · Oct 15, 2026

Trail Running Mandatory Gear Across 4 Races' Official RulesRUN GEAR NOTECompared by official specs2026.10.15Product image: Rakuten IchibaPictured (Rakuten Ichiba): Headlamp for trail runningTrail Running Mandatory Gear Across 4 Races' Official Rules80-lumen light, 1 L of water, 130×200cm blanket. I compare trail running mandatory gear lists across the official rules of 4 races. The base is 9 items required by 3 of the races, and 7 items have numeric specs, such as a light of 80 lumens or more for at least 4 hours, at least 1 L of water, and a blanket of at least 130×200cm. I also worked through the 2kg gear rule.Trail running · Oct 15, 2026

Best HYROX ApparelRUN GEAR NOTECompared by official specs2026.10.18Product image: Rakuten IchibaPictured (Rakuten Ichiba): PUMA x HYROX T-shirt / On Core-T / On Performance-T / On running shortsBest HYROX ApparelPUMA x HYROX vs On shirts, shorts and socks, compared by price. For HYROX, if running is your focus, go with On's Performance-T and lined shorts; if the stations come first, the Train Flex-T and Train Shorts. A top, bottoms and socks start at JPY 15,180.HYROX · Oct 18, 2026

Shoes & gearHow to Buy Japanese Running Shoes Overseas: Sizes, Duty, ShippingFour ways to buy Japanese running shoes from overseas: Rakuten forwarding, buying agents, local stores and shop-to-abroad shipping. How cm sizing works, US and Taiwan duty, banned items, from official pages.Oct 19, 2026

Brooks Ghost AMP ReviewRUN GEAR NOTEThe Shoe Nerd's Take2026.10.18Product image: Rakuten IchibaProduct pictured (Rakuten Ichiba): Brooks Ghost AMPBrooks Ghost AMP ReviewRelease date and how it differs from the Ghost 18. The Brooks Ghost AMP went on sale in Japan in late Aug 2026 at JPY 19,800. It weighs 250g (8.8 oz) in a 27cm and has a 6mm drop. That makes it 40g lighter than the Ghost 18, with a PEBA-blend DNA HYPE midsole. Here is what changed and how it fits.Shoes & gear · Oct 18, 2026

Adizero Adios Pro 5 vs HYPERWARP PURE 2RUN GEAR NOTEThe Shoe Nerd's Take2026.10.18Product image: Rakuten IchibaPictured (Rakuten Ichiba): Mizuno HYPERWARP PURE 2 (out Nov 6)Adizero Adios Pro 5 vs HYPERWARP PURE 2A 42g gap and different outsoles. The adidas Adizero Adios Pro 5 and Mizuno HYPERWARP PURE 2 differ by 42g at the same 27.0cm. Stack height is nearly identical; the plate placement and outsole rubber are not. I compare them down to who each one suits.Shoes & gear · Oct 18, 2026