Thermal underwear is in constant contact with your body, sweat, and the upper layers of clothing, so it needs to be washed more often than fleece or a winter jacket. And it is easy to ruin an item not by wearing it, but with a single improper cycle in the washing machine.
For most synthetic sets, a safe starting point is a delicate wash at 30 °C. But first, look at the label of the specific item: the fabric composition and allowed setting take precedence over general advice.
Polyester, polypropylene, merino, and blended materials require slightly different care. If you take this into account from the first wash, thermal underwear will retain its shape, elasticity, and proper fit for longer.
Spend two minutes preparing before washing
After 2–3 hours of active movement, do not leave damp thermal underwear folded in a backpack until the next day. It is better to take it out, let it air out, or prepare it for washing immediately. This is especially true for synthetic materials worn during a workout, hike, or intensive work.
Before putting it in the machine, turn the set inside out. This way, the inside, which is in direct contact with the skin, is washed better, and the outer surface rubs less against the drum and other items.
A few more simple steps before starting:
- check the pockets, if the design includes them;
- fasten the zippers and Velcro on other items you are washing together;
- do not put thermal underwear in the same cycle as jeans, clothing with metal hardware, or coarse fabrics;
- for a thin set, you can use a mesh laundry bag.
If the washing machine is rated for 7 kg, it does not mean you should pack the drum to the brim. For delicate fabrics, it is better to leave enough space so that the items can move freely in the water.
For synthetics, it is better to choose a low temperature
Polyester and polypropylene are often used in functional underwear because these fibers dry quickly and are suitable for active movement. They do not need high temperatures. For most synthetic models, a 30 °C setting with a moderate spin cycle will work. If the manufacturer allows 40 °C on the label, you can use that setting too, but there is no need to increase the temperature.
Washing thermal underwear at 60 °C "for better hygiene" can turn out to be too aggressive. Especially when the material contains elastane: regular heating and harsh cycles accelerate the loss of elasticity.
Imagine a set worn 3–4 times a week. Over a season, it goes through dozens of wash cycles. The difference between a delicate cycle and constant hot washing accumulates quite quickly.
It is better to leave fabric softener for other items
Regular fabric softener makes the fabric softer to the touch, but for functional clothing, this is not always a plus. Its components can remain on the fibers and affect how the material works with moisture. Therefore, for synthetic thermal underwear, we recommend using a liquid laundry detergent without fabric softener.
There is no need to pour a double dose of gel after a difficult hike or workout: the excess of the product is harder to rinse out completely from the fabric.
It is also better not to use chlorine bleaches. They are more aggressive to the fibers and dyes, and for regular thermal underwear care, such washing is simply not necessary. If after intensive use the smell remained after one cycle at 30 °C, run an extra rinse or a repeat delicate wash. This is safer than immediately switching to a high temperature.
Synthetics and merino require a different approach
Merino wool behaves differently than polyester. Hot water, aggressive rubbing, and strong wringing are especially undesirable for it.
You can follow this guide:
| Material | Temperature | Setting | Product | Drying |
|---|---|---|---|---|
| Polyester | 30 °C, unless the label allows otherwise | Delicate | Liquid, without fabric softener | Natural |
| Polypropylene | Around 30 °C | Delicate | Liquid | Without high heat |
| Merino wool | 20–30 °C | "Wool" or hand wash | For wool | Preferably flat |
| Blend with elastane | 30 °C | Delicate | Without bleach or fabric softener | Away from strong heat |
For merino, it is better to choose a special wool setting and a product designed for such fibers. After washing, do not wring the fabric by hand. You can gently blot the water with a towel, and lay the item flat on a horizontal surface.
A synthetic set is less demanding, but you should not "test its strength" with temperature and maximum spin either.
A dryer and a radiator can save an hour, but not the life of the item
After washing, you want to quickly put the set back in the closet, especially if the thermal underwear is needed the next morning. Synthetic materials dry quite quickly even without this.
Smooth out the item and let it dry naturally in a room with normal air circulation. Do not place damp thermal underwear directly on a hot radiator.
The surface temperature of the radiator can be significantly higher than the 30–40 °C that the fabric receives during a delicate wash. For materials with elastane, such local heating definitely does not add to their lifespan. With an automatic dryer, the rule is simple: use it only when the item's label expressly allows it. If there is no such indication, natural drying is safer.
How often to wash thermal underwear
There is no single number for all scenarios. After an intensive workout, a quick winter transition, or several hours of active work, it is better to wash the set after use. If you wore the thermal underwear for 1–2 hours for a leisurely walk, it remained dry and clean, sometimes it is enough to just air it out well. This is especially relevant for merino wool: such a material often does not require washing after every short outing.
Focus on the actual condition of the item, not on the calendar. A noticeable smell, traces of sweat, or stains are a normal reason to send the set for washing.
Five mistakes that shorten the life of thermal underwear
Most care problems are repeated. A set can withstand 20–30 delicate cycles well, but lose its shape much faster if you regularly wash it in a towel setting. Most often, high temperature, fabric softener, bleach, maximum spin, and drying on a hot radiator are harmful. Another typical situation is when thermal underwear goes into the drum together with jeans, clothing with Velcro, and items with coarse zippers.
No complicated care ritual is needed here. For a synthetic set, 30 °C, a delicate cycle, a liquid detergent, and natural drying are usually enough. For merino, we add a wool setting and handle the wet fabric more carefully.
Proper care makes sense from a practical point of view too: functional clothing is not bought for a few outings. If the fabric retains its fit longer, does not stretch after washing, and works normally under load, the set does not have to be replaced prematurely.
If you are choosing new thermal underwear or are unsure how to wash a specific model, write to us before the first wash. Our manager will help clarify the material, the care setting, and select a set for your usage scenario — consultation and selection are part of our service, not an additional option. You can choose new thermal underwear in the catalog: men's thermal underwear and thermal underwear for women.
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