Millet remade its active thermal line on September 30, 2026, adding the Sol Thermo and Hydro Dry. Choose the Sol Thermo for lightness and warmth in the sun, and the Hydro Dry if drying out comes first on sweaty climbs.
The Gear Nerd's Pick
These two series get their warmth from different places. The Sol Thermo uses a material that turns near-infrared sunlight into heat; the Hydro Dry uses a material that spreads sweat fast so it dries. That's why I recommend the Sol Thermo to people walking sunny ridges and the Hydro Dry to people facing lots of steep, sweaty climbs.
Key points
- The Sol Thermo Crew is ¥18,700 and 164g. The Hydro Dry Crew is ¥15,400 and 196g: ¥3,300 cheaper and 32g heavier
- The Sol Thermo showed a temperature rise of up to 12.8℃ in Millet's own tests. The Hydro Dry claims about 1.8 times faster drying than polyester
- Both are regular fit in Euro sizing. Sol Thermo: XXS to XL; Hydro Dry: XS to XL
When did the Millet Sol Thermo and Hydro Dry come out?
Millet has remade its active thermal line. The Sol Thermo and Hydro Dry are available from Sep 30, 2026 at the official online store and retailers nationwide in Japan. They're new and already on sale.
Active thermal layers are thin warm layers you wear while walking. Their role differs from down you pile on when you stop. For the layer against your skin, see my base layer rankings.
How I chose
The first thing I looked at was where the warmth comes from. The Sol Thermo uses a material that turns near-infrared sunlight into heat, and the Hydro Dry a material that spreads sweat so it dries: both 'warm layers,' but with different aims. Next I lined up weight and price. What gave me pause was whether to recommend the Sol Thermo at ¥3,300 more. Paying for its lightness and warmth in the sun makes sense for people walking sunny ridges. For heavy sweaters, the cheaper Hydro Dry, built to dry fast, makes more sense.
Image: Rakuten Ichiba
Millet Sol Thermo Crew
Lowest price on Rakuten: ¥18,700 (as of 10/15). Prices change daily.
RecommendedSee it on RakutenSee it on Yahoo! Shopping JapanWhat's the difference between the Sol Thermo and Hydro Dry?
| Style | Official price | Weight (M) | Material |
|---|---|---|---|
| Sol Thermo Crew | ¥18,700 | 164g | Solament Heat, 100% polyester |
| Sol Thermo Half Zip | ¥19,800 | 178g | Solament Heat, 100% polyester |
| Hydro Dry Crew | ¥15,400 | 196g | 73% polyester, 27% polystyrene |
| Hydro Dry Zip | ¥16,500 | 212g | 73% polyester, 27% polystyrene |
Comparing the crews, the Sol Thermo is ¥3,300 pricier and 32g lighter (196g − 164g). Price per gram is about ¥114 for the Sol Thermo Crew (18,700 ÷ 164) and about ¥79 for the Hydro Dry Crew (15,400 ÷ 196).
What's good about the Sol Thermo? A light warm layer that uses heat from the sun
It's a material that absorbs near-infrared sunlight and stores heat inside your clothing. In Millet's own tests, it rose by up to 12.8℃. It's a thin brushed mesh, highly breathable, and built to let excess heat escape.
The crew is light at 164g and suits people who want to cut pack weight. This part is so-so. Because the material takes in heat, this feature doesn't work on cloudy days or in shaded stream valleys. The Half Zip (178g) is for people who want to regulate body heat with a zipper.
What's good about the Hydro Dry? It dries sweat to keep the chill down
An active thermal layer for hiking that pulls sweat off your skin fast and spreads it outward, keeping you warm in low temperatures while staying dry. Its Epsilon material claims about 1.8 times faster drying than polyester.
Prices start at ¥15,400, an easy price for an active layer on sweaty climbs. At 196g, it's heavier than the Sol Thermo. The Zip (212g), with a longer front zipper, is the style to pick for easy venting.
Image: Rakuten Ichiba
Millet Hydro Dry Crew
Lowest price on Rakuten: ¥15,400 (as of 10/15). Prices change daily.
RecommendedSee it on RakutenSee it on Yahoo! Shopping JapanWhich to pick? Who each style suits
- If you mostly walk sunny ridges or low mountains on clear days: the Sol Thermo Crew. Take the 164g lightness.
- If you want to regulate body heat with a zipper: the Sol Thermo Half Zip or the Hydro Dry Zip.
- If you sweat a lot or want a cheaper start: the Hydro Dry Crew.
Image: Rakuten Ichiba
Millet Hydro Dry Zip
Lowest price on Rakuten: ¥14,850 (as of 10/15). Prices vary by shop, up to ¥17,100, and change daily.
RecommendedSee it at L-BreathSee it on RakutenSee it on Yahoo! Shopping JapanWho is it for?
The Sol Thermo suits people who want to walk sunny autumn ridges or sunlit low mountains in winter in as light a layer as possible. The 164g crew uses a material that turns sunlight into heat, so it goes after warmth without adding weight. Of Millet's new gear this autumn, it's the build I found most interesting.
The Hydro Dry suits people whose problem is sweating on steep climbs and getting chilled on breaks. Its material spreads sweat so it dries, and with prices from ¥15,400, it's easy to try.
If you want to match the waterproof layer on top with the same brand, the brushed-lined jacket in my Millet Typhon Warm review is a candidate to pair with it. For a warm layer you put on when you stop, down is another option.
If your current insulating mid layer gives you no trouble with weight or drying, you don't need to add one.
FAQ
When were Millet's active thermal layers released?
Millet has been selling them since Sep 30, 2026.
What's the difference between the Sol Thermo and the Hydro Dry?
The Sol Thermo uses a material that harnesses heat from sunlight and is lighter (crew 164g); the Hydro Dry uses a material that dries sweat, is a bit heavier (crew 196g), and costs less.
What sizes does the Sol Thermo come in?
Six Euro sizes, XXS to XL. The Hydro Dry is XS to XL. Both are regular fit.
