Thermal Underwear Test: Thermal Retention Value Variations by More than a Double, Sweat Wicking and Quick Drying Performance in Nearly Half the Samples Unsatisfactory

15 January 2018
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To beat the bitter winter cold, consumers have shown a growing preference for thermal underwear of synthetic fibres that are lighter and more airy, offering warmth and comfort, to pure wool or cotton or other thick heavy apparels. The Consumer Council has put to test 20 different models of thermal daily wear and sports or outdoor activities wear, which were found to vary with a difference of more than double in thermal retention value. Furthermore, nearly half (8 samples) performed poorly in sweat wicking and quick drying – which are essential to the wearer’s comfort. Significant variations were detected also in their durability with nearly 30% of the samples’ resistance to pilling rated at only 2.5 points or below, and some were found in relatively large dimensional changes after repeated washing.
 
Covered in the test were 20 men and women long-sleeved thermal underwear comprising 15 for daily wear and 5 for sports or outdoor activities wear – and ranging in price from $99 to $559 with focus on: thermal retention, water vapour permeability, sweat wicking and quick drying performance, and durability. The overall rating in performance, with the highest score of 5, showed that all of the sportswear models were rated at 4 points or above while the daily wear models fared comparatively less satisfactory with only 60% (9 samples) scoring 4 points or above.
 
Consumers are advised to choose according to their own individual needs. For instance, if you are cold sensitive and seldom exercise, you should consider a daily wear model with good thermal retention performance. On the other hand, if you enjoy an active physical lifestyle with frequent perspirations, or have to work for long hours in windy or cold conditions outdoors or engage in strenuous exercise, your choice should be a sportswear model that provides better performance in water vapour permeability, sweat wicking and quick drying; their durability is generally higher but so are their prices.
 
The variation in the daily wear samples’ thermal retention value between the least and top performers was found respectively 0.12 clo and 0.23 clo, a difference of nearly double. In the case of sportswear models their thermal retention value varied even more noticeably from 0.1 clo to 0.32 clo, a difference of more than twofold; further, the highest-priced ($559) and another men sportswear (about $300) both had their thermal retention value measured at only 0.1 clo, the lowest of all test samples. Consumers are reminded that the test results indicated that there is not necessarily a direct correlation between the price and the thermal retention value of the products. 
 
 
To evaluate the thermal retention ability after washing, the underwear samples were subjected to 30 repeated washings. The results showed the great majority remained intact and were not reduced in any way in thermal retention value; in fact one sample rose from 0.1 clo before wash to 0.28 clo after wash, an increase of 1.8 times. It is believed the washing has loosened up the fabric tissues, thus trapping in more air and warmth to avoid the loss of heat. In contrast, a sample had its thermal retention value after 30 washings dropped from 0.15 clo to 0.06 clo, a reduction of 60%.
 
The test also examined their water vapour permeability, sweat wicking and quick drying ability on how effectively could the underwear fabrics expel the water vapour on the skin, absorb and transfer the perspiration from the skin to the fabric surface for evaporation – to avoid moisture being trapped between the skin and the underwear, leading to feeling hot and damp. Or in the cold outdoors, the perspiration will cause the body temperature to drop, giving rise to a feeling of wet and cold. In the water absorption speed test, with the exception of the 8 poorly-rated samples which took more than     1 minute to completely absorb the water beads, most of the remainder samples were able to complete the process in just 1 to 2 seconds indicating such products are more ideal for sportswear as they can absorb sweat from the skin effectively. But in one women’s sportswear model, the innermost layer (the surface in contact with the skin) of its main fabric material needed more than 1 minute to complete the water absorption in the test, and thus scored only 1 point.  
 
For speed in moisture evaporation, apart from the 8 poor water absorption samples, the time required to restore from completely wet to completely dry of the samples varied by over a double, from 121 to 261 minutes. In general, the daily wear models were faster in evaporation speed ranging from 134 minutes to 216 minutes. Among the sportswear models, with the exception of the one sample requiring 121 minutes, the remaining 4 samples all needed more than 220 minutes to completely evaporate the moisture in the test. Samples with slower moisture evaporation speed generally used thicker fabrics, resulting in more moistures retained and thus more time to fully dry off.
 
On durability, the tests focused on their bursting strength, resistance to pilling and changes in dimensions and appearance after wash. In the bursting strength test, the majority of the models performed well with a rating of 5 points in full; only 2 others were relatively weaker with 4.5 and 3 points; and another one could not complete the test probably due to the high elasticity of the fabric. The samples were also subjected to rubbing 125, 500 and 2,000 revolutions, for assessment of their extent of pilling. The test showed 4 sportswear models to achieve resistance to pilling with a top score of 5 points; while 6 other samples were rated with only 2.5 points or below. After 30 times of washing, practically all samples were found shrunk or became longer or broader to various extent. 2 samples in particular recorded a shrinkage rate of some 5% – in the sleeve cuffs, neck collars, and upper arm areas.
 
Consumers are suggested to take heed of the following:
  • Underwear that uses pile or fleece fabrics are better in thermal retention than other materials and therefore are suitable for people particularly sensitive to cold; 
  • Fluffy fabrics allow more air to be retained in the fibres and are more effective in preventing heat loss. Softer underwear also offers better comfort to the wearer;
  • People habitually sweating a lot should choose underwear with good sweat wicking and quick drying performance;
  • For those prone to skin allergy or irritation or suffering from eczema, consider the choice of underwear made of pure cotton or blended fabrics with cotton as the main component.   
 
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