Thermal underwear is a base layer worn directly against the skin, designed to retain body heat and wick away sweat and moisture. It acts as a second regulating layer: it insulates against external cold and keeps the skin dry, preventing the body from unnecessarily losing heat. It is the first item to choose when temperatures drop, whether for sports or everyday life.
What is thermal underwear and how does thermoregulation work?
Thermal underwear is a technical garment worn in direct contact with the skin, designed to work on two fronts simultaneously: thermal insulation and moisture management. The fabric traps a thin layer of warm air close to the body, reducing heat dispersion to the outside; at the same time, the fibers push sweat to the outside of the garment, where it evaporates faster. This dual mechanism is called thermoregulation: it keeps the skin dry and body temperature stable, avoiding both the cold from stagnant sweat and overheating during movement.
It's not just a matter of "covering up more": effective thermal underwear actively works with the body, while a normal garment, like one made of pure cotton, retains moisture and promotes skin cooling.
When should you wear thermal underwear?
Thermal underwear is useful whenever the temperature drops below usual comfort levels, not just during sports:
- Outdoor sports activities: running, cycling, skiing, trekking
- Daily life in cold months, under trousers and sweaters
- Mid-seasons (autumn, early spring), as a light garment worn alone
- Poorly heated environments, office or home, where warmth is needed without bulk
On colder days, it acts as a first layer under other garments; in mid-seasons, it can be enough on its own, thanks to its snug and lightweight fit.
What are the differences between Risalti's thermal underwear lines?
Risalti offers four lines of thermal underwear, each designed for different levels of cold and use. The main difference is between technical fiber and natural fiber: the Energy and Extreme lines focus on high-performance technical fabrics, while Merino Wool and Tech+ use merino wool for natural warmth.
Energy: the lightweight technical line
Energy is made with SoftAir Plus® yarn, soft and light on the skin. It is designed for a temperature range between +5°C and +20°C, suitable for dynamic sports activities and everyday use in mid-seasons. The antibacterial treatment makes it suitable for extended daily use.
Merino Wool: natural warmth
The Merino Wool line uses natural fiber, which passively regulates body temperature and stays warm even when slightly damp. It is the most suitable choice for those looking for warm underwear for everyday use, at home or outdoors, with a soft and natural feel against the skin.
Tech+: the blend of nature and technology
Tech+ combines merino wool fiber with technical yarns, creating a garment that retains the natural warmth of wool with greater resistance and elasticity. It is suitable for those who want the benefits of merino wool in a garment also designed for movement.
Extreme: for intense cold
Extreme is the highest-performing line, designed for temperatures between -5°C and +10°C. The technical fabric offers more pronounced compression and superior insulation, suitable for winter sports, mountains, and intensely cold days.
Which thermal underwear line to choose based on the cold?
The following table summarizes which Risalti line to choose based on temperature and intended use:
| Line | Ideal temperature | Recommended use | Material |
|---|---|---|---|
| Energy | +5°C / +20°C | Dynamic sport, mid-season, daily use | SoftAir Plus® technical yarn |
| Merino Wool | Moderate-intense cold | Daily use, home, natural comfort | Natural merino wool |
| Tech+ | Moderate-intense cold, in motion | Sports and outdoor activities requiring elasticity | Merino wool + technical fiber |
| Extreme | -5°C / +10°C | Winter sports, mountains, intense cold | High-compression technical fabric |
How to choose the right thermal underwear?
To choose the right thermal underwear, it is advisable to consider three factors together, not just one:
- Activity: intense sport and outdoor activities require breathable technical fabrics (Energy, Extreme); daily use and home comfort are better suited to merino wool.
- Temperature: the more intense the cold, the heavier and more insulating the line needed (Extreme, Merino Wool); for mid-seasons, a light garment is sufficient (Energy).
- Fit: thermal underwear should cling to the body without compressing, without folds or gaps, to ensure insulation; flat seams and seamless design reduce chafing and improve comfort under other garments.
If in doubt between two thicknesses, it is preferable to choose the snugger model: a thinner but well-fitting layer insulates better than a thick but loose one.
How to combine thermal underwear with other layers?
On intensely cold days, thermal underwear works best within a layering system: a snug first layer (the thermal underwear itself), an insulating second layer like a fleece or sweater, and an outer layer that protects against wind and rain. The first layer must remain close to the skin to effectively manage moisture; if it is too loose, warm air disperses more easily and breathability loses effectiveness. On milder days, or during low-intensity activities, thermal underwear can be worn alone, without additional layers, taking advantage of its lightness and snug fit to stay comfortable without excessive sweating.
Why does seamless technology improve the comfort of thermal underwear?
Seamless technology produces garments without side seams, using a single tubular process that eliminates the most common friction points on hips, crotch, and cuffs. For a garment worn in contact with the skin for hours, like thermal underwear, this detail directly affects comfort: no marks under tight clothing, no chafing during movement or sports. Risalti produces its thermal underwear in Castel Goffredo, in the province of Mantua, a historic Italian hosiery district, using OEKO-TEX certified fabrics: direct control over every phase, from yarn selection to finishing, which results in flat seams and consistent fit wash after wash.
Men's, women's and children's thermal underwear: what's the difference?
The operating principle is the same, but the fit and models are designed for different needs. For women, the women's thermal underwear collection includes leggings, tops, and tights, with a snug fit and seams designed for the female body: among the most requested are the Energy thermal leggings for women, for sports and mid-season, and the Merino Wool thermal leggings for women, for intense cold and daily use.
For men, the men's thermal underwear collection offers models with the same technical logic, such as the Merino Wool thermal leggings for men, suitable for those seeking natural warmth with a more structured fit.
For those seeking maximum insulation in intensely cold conditions, the Extreme leggings are designed for winter sports and particularly harsh days.
For children, thermoregulation is even more important because the body loses heat more quickly: the children's thermal underwear collection offers garments like the Energy thermal vest, light and breathable for school or outdoor play.
Those looking for targeted warmth on legs and ankles can combine the Merino Wool thermal knee-highs or the Merino Wool thermal cycling shorts, comfortable under boots or winter running shoes.
How to wash thermal underwear without damaging it?
Care depends on the material. Technical fiber thermal underwear (Energy, Extreme) should be machine washed at low temperatures, around 30°C, with delicate detergents and no fabric softener, which reduces the fabric's breathability. Merino wool requires more attention: it should be washed cold or at a maximum of 30°C, with a delicate cycle or by hand, avoiding aggressive spinning and tumble drying, which can felt the fiber. In both cases, it is best to air dry, away from direct heat sources, to preserve the garment's elasticity and thermal capacity over time.
Frequently Asked Questions about Thermal Underwear
Does thermal underwear make you sweat more?
No, on the contrary: technical fabrics and merino wool are designed to wick moisture away from the skin and promote evaporation, keeping the body dry even during physical activity.
Can thermal underwear be worn every day?
Yes. In colder months or poorly heated environments, daily use is recommended, alternating garments to allow for washing and maintain skin hygiene.
Is merino wool better or a technical fabric like Energy?
It depends on the use: merino wool offers natural warmth and comfort for daily use and intense cold, while a technical fabric like Energy is lighter, more elastic, and suitable for sports and mid-season.
What is the difference between Extreme and other Risalti lines?
Extreme is the line designed for the most intense cold (-5°C / +10°C), with superior compression and insulation compared to Energy, Merino Wool, and Tech+, which are designed for a more moderate temperature range.
The Right Choice, Season After Season
There is no single "best" thermal underwear: there is only the one most suitable for the temperature, activity, and your skin. By evaluating these three factors together, and choosing from the Energy, Merino Wool, Tech+, and Extreme lines, you can stay warm and dry in any condition, without sacrificing comfort. For a broader comparison between thermal underwear brands available on the market, our guide on the best thermal underwear brands delves into selection criteria, from material to Made in Italy.
