We have tested these 10 products
- Ocean Pro+ functional underwear, Brand: AW Niemeyer
- Hydrophobic thermal top and trousers, Brand: Gill
- Men's leggings and top with round neck, Brand: Gill
- Lifa Merino Midweight 2-in-1 Base Layer, Brand: Helly Hansen
- HPX Merino Base Layer, Brand: Musto
- Thermal base layer top and trousers, Brand: Musto
- Core Base Layer Top and Pant, Brand: Zhik
- Superthermal Hydrobase, Brand: Zhik
- Reference Underwear Top and Pant, Brand: Sailracing
- Racer 500 functional shirt and trousers, brand: Tribord
Everyone knows it from sport: after an intense workout, you need to put on something warm during the subsequent resting phase, even if you are sweating and very warm. On board, this situation occurs after manoeuvres, such as tacking, setting and trimming the spinnaker, when you are sitting quietly in the cockpit afterwards.
The human body is very good at maintaining a constant body temperature. However, during extreme changes between intense activity and rest, the right clothing must be worn to help. This is because the body's own regulation technology can protect against hypothermia and overheating by changing the blood flow to the skin muscles (goose bumps) and sweat production. Sweat plays a particularly important role in the latter. Wet skin is cooled by evaporation. This is very important during high levels of activity, but if a period of rest follows abruptly, you quickly cool down too much. This risk is all the greater in the cold season, at night or in strong winds.
Thermal underwear important for well-being
The regulation of body temperature directly influences whether we are warm or cold and is therefore crucial for our well-being. The most important item of clothing here is functional underwear, also known as a base layer.
Thermal underwear, functional underwear, first layer or base layer all refer to the same item of clothing. The last two names refer to the combination of different textiles in superimposed layers to withstand low temperatures. The first layer is the one that lies directly on the skin. Its task is to wick away moisture and thus provide important protection against freezing. To ensure that perspiration is quickly removed from the body, the functional underwear must fit snugly and absorb moisture directly. As the absorption capacity of the fabric is limited, the material must be designed in such a way that moisture is quickly released to the outside. This means that the bottom layer of clothing not only keeps you warm, but the evaporation on its surface also cools you down. It's all about the right timing: if it takes a long time to release the moisture, the clothing will feel clammy or even wet when more sweat is added. If the moist air is released more quickly, the clothing cools you down when you sweat, but warms you immediately when you are less active, as the moisture does not accumulate in the fabric. The faster the material of the clothing can release moisture, the better it helps to regulate body temperature.
Polyester and wool with advantages and disadvantages
There are various synthetic and natural fibres that are particularly suitable for base layers. Polyester has the advantage that the fibre itself does not absorb moisture. The sweat droplets are absorbed by the fabric and can evaporate quickly thanks to the large surface area of thousands of fibres. In addition, polyester textiles feel pleasant on the skin, are light and resistant. The only disadvantage is that bacteria that feed on human sweat settle particularly well on synthetic fibres and their excretions cause unpleasant odours. Special coatings or admixtures of polypropylene or polyamide fibres can counteract the formation of odours.
The natural fibre wool is highly functional. Sheep's fur has ideal properties for thermal underwear. Its surface repels water, but the inside of the fibre can absorb moisture. As a result, wool fabric still feels dry even when it is damp and thus regulates the climate in the garment - a natural breathability.
Wool is also naturally antibacterial and bad odours do not develop so quickly. And if they do, they can simply be removed by airing. Two further plus points that can influence the purchase decision: Wool is a renewable raw material and, unlike synthetic fibres, no microplastics are released into the environment during washing.
However, there are also disadvantages. Not everyone likes the feel of wool on the skin and it can be a little scratchy. In addition, special care must be taken when washing (albeit rarely) to ensure that the fibres do not become matted or even shrink. And wool can pill, i.e. form small knot-like fluffs. Merino wool is particularly suitable, but also expensive, as it hardly scratches and can transport a lot of moisture.
10 combinations for thermal underwear in the test
The test field consists of ten clothing combinations (top + trousers) from manufacturers and retailers that are established in water sports. There would be significantly more manufacturers for thermal underwear if products for other sports were also included. Ski underwear, for example, fulfils the same purpose. However, the test would then have become very confusing.
Eight base layer sets are made of synthetic fibre. They come from AWN, Gill, Musto, Sailracing, Tribord (Decathlon's own brand) and Zhik. The HPX Merino from Musto and the Lifa Merino from Helly Hansen are made either entirely (Musto) or partially (Helly Hansen) from natural fibres.
Two combinations of thermal underwear stand out: the Gill Hydrophobe can be worn both as a light protective layer (rashguard) in warm temperatures and, when it's colder, under a wetsuit when dinghy sailing or surfing. It also has UV protection. The second exception is the Superthermal Hydrobase from Zhik. It is made from a much thicker fabric than all the other test candidates and is also said to be suitable for particularly low temperatures. Apart from a few details such as reinforcements on the knees, elbows and buttocks, different collar shapes or an opening, the base layers in the test are quite similar.
Fit, breathability and drying behaviour of the thermal underwear
Three values are particularly important in the test setup: the fit, which is a prerequisite for the base layer to function. This was determined by trying it on. Breathability, i.e. the transport of moisture, which we analysed using thermal imaging. We also examined the drying behaviour. To do this, the clothing was weighed when dry, wet and during drying after five and ten hours. This allowed us to determine the amount of water in the fabric. The good news: after ten hours, all the garments in the test were dry again. This means that if they have been very wet or washed, they can dry overnight and be ready for use again the next day. The price and good details were also taken into account in the assessment.
The fit was very good with four base layers: the Hydrophobe from Gill, the HPX Merino from Musto, the Racer 500 from Tribord and the Core Base Layer from Zhik fitted the body best. However, most of the other test participants were also good at this, only the Ocean Pro+ from AWN had no body-hugging cut at all. This can also be seen in the thermal images (see below): As the top and trousers are barely snug, very little body heat is released. The air cushion insulates well, but sweat is not absorbed by the skin. Depending on the activity, it is either too warm or too cold in this clothing.
This leads directly to the next point in the test: the infrared images. It is not the primary task of functional underwear to insulate. That's why red (i.e. warm) areas in the images are not bad. The difference between the two images is important. The top thermal image in the table was taken one minute after the base layer was put on. The second image below was taken after a fixed period of time during which a small, always identical sports programme was completed. The activity caused the body temperature on the skin to rise and sweat to form. The second image therefore shows how well the tissue can absorb and release the excess heat energy. The greater the difference between the first and second absorption, the better.
The differences between the thermal underwear garments are also interesting. For example, the Superthermal Hydrobase from Zhik is simply much thicker than all the other base layers in the test: the thermal image is almost exclusively blue and green, i.e. rather cold. All items of clothing in the hip area are also more heavily insulated. The trousers and top overlap here. It is advisable to tuck the top into the trousers, firstly because it won't slip during activity and secondly because it fits better and therefore transports moisture better. In terms of drying behaviour, the measured values in the table show that the Reference Underwear from Sailracing has the best values. The fabric absorbed almost half of its own weight in moisture and released 75 per cent of it again after five hours. The Superthermal Hydrobase from Zhik, the leggings and top from Gill, the thermal base layer from Musto and Tribord's Racer 500 are similarly good.
The Hydrophobe from Gill is a special case. It only stored around ten per cent of its own weight in moisture, but released this almost completely after just five hours. Surprisingly, it still felt clammy on the outside. In contrast, the HPX Merino from Musto retained even more moisture after the five hours, but it already felt dry. This shows the different material properties of thermal underwear.
Pleasing result of the test
At the end of the test, the result is pleasing: many of the base layers tested are very good to good, so there is plenty to choose from. The top products are the Core Base Layer from Zhik (test winner), Sailracings Reference Underwear, Mustos Thermal Base Layer and leggings and top from Gill. The Racer 500 from Tribord also has very good values and is also extremely attractively priced, making it the price-performance tip. The HPX Merino from Musto was not included in the top group because it plays a special role: At a total of almost 280 euros, it is the most expensive clothing set in the test. The merino wool cannot quite keep up with the drying values of the polyester fibres, but makes up for this with its special properties. The HPX Merino is by far the lightest functional underwear in the test and fits super comfortably.
The Hydrophobe from Gill also has a special status. Due to the different material composition, it feels clammy more quickly, but dries very quickly. Its advantage is its wide range of uses: it can also be worn as an outer layer on the SUP in the anchor bay or under a wetsuit at lower temperatures, thus fulfilling three functions at once. We can recommend both the inexpensive item from Tribord and the rather expensive HPX Merino. If you tend to be out and about in nice weather in summer and only wear functional underwear twice a year, you can't go wrong with the price-performance tip. For all those who start the season as early as possible in frosty temperatures, don't shy away from night rides even in mixed weather and spend half the season in their base layer, the premium merino piece can also be a recommendation. The leggings from Gill are a very good alternative here. They are priced somewhere between the extremes, but are top quality.
And on waking or after a day's sailing, the base layer becomes the sailor's jogging trousers when the mid layer and oilskins are already hanging in the wardrobe. On cold nights, the base layer is also suitable as pyjamas that you won't want to take off at all.
Under and over
Three layers of clothing form the basis for a balanced body climate at low temperatures. The base layer has the task of keeping the skin dry and wicking away moisture. To do this, it must fit snugly. The mid layer, also known as the body warmer, should not be too tight, is more insulated and stores body heat in the air pockets. Nevertheless, it must be permeable enough to allow moisture to pass through to the outside. Finally, the oilskin follows on the outside. It protects against penetrating moisture such as rain or spray, but still lets moisture out from the inside thanks to the breathable membrane. If it gets particularly cold, additional warm layers can of course be added or thicker ones used. However, products with a membrane are not recommended. Two membranes would delay the removal of moisture.
This is how we tested
We checked the fit by trying them on and the drying behaviour by weighing the garments when dry and wet. The base layers were soaked in the washing machine, and by spinning them gently, enough moisture remained in the fabric so that it no longer dripped and remained comparable. The infrared images were taken in a barn at a constant twelve degrees Celsius. Particular attention was paid to ensuring that the starting conditions were always the same: before each run, the tester had a break at room temperature to avoid hypothermia. The base layer was then put on and the first thermal image was taken. This was followed by three minutes of exercise and the second photo was produced. We also took price and workmanship into account.
