What the research says
The most direct question is whether a quick dry fabric changes how hot you get. A narrative review covering studies of 15 to 120 minutes, at 20 to 70% of maximal oxygen uptake and 18 to 40 °C, concluded that few studies have identified significant differences in body temperature, perception or performance between natural and synthetic fabrics, or between chemically treated and untreated versions of the same cloth (Di Domenico et al., 2022). The authors also noted that trials rarely reproduce the hot, humid, long sessions that endurance athletes face, and called for tests at 30 °C or above, 70% humidity or above, and beyond 45 minutes.
Individual trials back that up. In a crossover study of eight trained men running for 30 minutes at 70% of maximal oxygen uptake at 30 °C and 35% humidity, an evaporative polyester ensemble and a cotton one showed no differences in mean body, rectal or skin temperature, in heart rate or oxygen use, or in comfort sensations (Gavin et al., 2001). Another group of eight men ran at 31.7 °C and 42% humidity in polyester shirts with 4, 6 or 8 channels or in cotton; skin, core and body temperatures did not differ while running, nor did heart rate, lactate, time to exhaustion or the sense of clothing wetness; during recovery, body temperature and shivering/sweating sensations were lower in the 4- and 6-channel polyester shirts (Sperlich et al., 2013).
A 45-minute treadmill run at 60% of maximal oxygen uptake and 32 °C, comparing cotton, a cotton and soybean blend and a polyester with mesh loops, again found no clothing effect on rectal, skin or body temperature, heart rate, in-session ratings of perceived exertion or comfort (Davis et al., 2017). Outdoors, six men and six women ran 10 km in white or black polyester or cotton shirts; pace, heart rate, rectal and skin temperatures did not differ, although the Physiological Strain Index was higher in the cotton conditions (De Alcantara Borba et al., 2016). A small pilot of seven physically active men with obesity, walking for 30 minutes at 27 °C, found only one forehead temperature difference between polyester and cotton and no difference in perspiration, so the authors did not support either fabric as superior (Masoud et al., 2023).
Where fabric does show a difference: the microclimate
Dai et al. (2008) use the term microclimate for the space between the garment and the body. Even when core temperature was unchanged, some trials found that this space behaved differently. In the 31.7 °C running study, relative humidity at the chest and back was lower in every polyester shirt than in cotton, and body temperature during recovery was lower in the 4- and 6-channel shirts (Sperlich et al., 2013). In the 32 °C study, chest microenvironment temperature was lower in the synthetic clothing, and session ratings of exertion and thermal sensation were also lower, even though the main comfort scores were not (Davis et al., 2017).
A laboratory study of wicking and wear found something similar for a soybean-protein and cotton blend that wicked well: vapour pressure under the T-shirt rose later and stayed lower, and skin temperature under the shirt was lower than with plain cotton. The authors concluded that moving water along the fabric matters more than soaking it up (Dai et al., 2008).
Sweat retention and the recovery period
Two of the trials described here reported how much sweat the shirt retained, and both reported less in polyester than in cotton. In the first, eight men completed three 20-minute bouts at 8 km/h in 25 °C and 60% humidity. Polyester gave a higher sweating efficiency and left less moisture in the shirt than cotton, although thermal sensations during exercise were similar. After exercise, skin temperature returned to its starting level faster in polyester, and the men reported weaker shivering or sweating sensations (Brazaitis et al., 2010).
In the second, a hotter test, ten men exercised for 45 minutes at 50% of peak oxygen uptake in 33 °C and 60% humidity. A form-fitted shirt of 81% polyester and 19% elastane retained less sweat than cotton and was linked to a lower rectal temperature during the final 15 minutes (De Sousa et al., 2014). This is one of the few trials in which temperature itself moved, and it is a single study of ten men wearing a shirt.
Conditions matter too. Twelve men cycled at 15 °C and 50% humidity and then went through a drying phase in a windy chamber. A wool shirt kept torso skin temperature higher than cotton, viscose or polyester and was rated more comfortable afterwards (Abedin and DenHartog, 2024). This is one small study of 12 men in cool conditions and says nothing about shorts.
Stickiness and fabric saturation
Comfort is not the same as physiology. In a study of wetness and stickiness during exercise, fabrics with a higher saturation percentage felt stickier, even when they touched less skin and held less sweat in absolute terms. Perceived wetness did not change between fabrics with different saturation, contact area and sweat content. Texture was the leading predictor of discomfort at the start, and stickiness was the leading predictor once exercise began (Raccuglia et al., 2018). The abstract does not give the number or type of participants.
This is our reading rather than a result reported by Raccuglia et al., whose abstract does not mention quick dry fabrics: a fabric that stays less saturated might feel less clingy. That would be a comfort effect only, and the trials above do not show that it changes core temperature or performance.
Thickness and evaporative cooling
Experiments with a sweating torso manikin tested one-layer, tight-fitting sportswear in a hot setting. The real evaporative cooling efficiency fell in a straight line as more moisture moved from the skin into the clothing layer, with a close linear fit (adjusted R-squared above 0.97). Thicker fabric had a negative effect: a thick merino wool performed worst, while a 100% polyester fibre and a 50/50 wool and polyester blend kept efficiency up (Wang et al., 2014). The authors suggested thin materials for one-layer, tight-fitting sportswear.
Knit structure, stretch and breathability
Fabric properties also depend on yarn and knit structure, not only on fibre names. A correlation analysis of knitted sportswear fabrics found that yarn linear density, short protruding fibres and fabric weight per area had the largest influence on heat resistance, while yarn linear density, longer protruding fibres and fabric thickness had the largest influence on air permeability (Salopek Čubrić et al., 2022).
Researchers comparing four elastic knitted fabrics for cycling wear measured air permeability, moisture management, drying time, thermal conductivity and water vapour permeability together. A polyamide and elastane knit (58/42) combined good air permeability and moisture management with a short drying time, and the authors judged it better suited to summer cycling clothing (Teyeme et al., 2020). The point is that stretchy fabrics are not all alike, and that drying time can be measured rather than assumed.
Odour and sun protection: secondary effects
A 2023 review noted that sportswear worn against the skin is easily soaked by sweat and can become a breeding ground for skin microbes that generate odour. It covers quick-dry technologies and odour management, including antibacterial treatments and adsorbent materials (Chang and Wang, 2023). The abstract links sweat-soaked sportswear to odour-causing microbes and does not report whether quick-dry fabric reduces smell.
On sun, tests of 34 polyester sports T-shirts found that more than 75% reached an excellent protection factor of 40 to 50 or more, that the density of the weave (cover factor) was the main determinant, and that wetting or sweating raised the protection factor by over 20%. Colour made no difference to the protection factors (Aguilera et al., 2023). That is a statement about those shirts, not about shorts. These are laboratory fabric measurements for those T-shirts, not a claim about any Free Muscle garment.
Stretch and fit: how little is tested
Stretch claims are usually about freedom of movement, and the evidence here is the thinnest. The one relevant study looked at 28 young adults in work tasks such as lifting, squatting with a liquid container and reaching, wearing trousers that were too small or correctly sized. Low-back discomfort ratings were higher in the tight trousers, while lumbar range of motion was higher and erector spinae activity lower (Eungpinichpong et al., 2013). In that study, trousers that were too small were rated as more uncomfortable at the low back; it says nothing about gym shorts or stretch fabric.
Key studies at a glance
| Study |
Who and what |
Main finding |
| Di Domenico et al., 2022 |
Narrative review of sports clothing in the heat |
Few significant differences between natural and synthetic fabrics; calls for hotter, longer tests |
| Gavin et al., 2001 |
8 trained men, running, 30 °C |
No difference in temperature, heart rate or comfort between polyester and cotton |
| Sperlich et al., 2013 |
8 trained men, running, 31.7 °C |
Lower chest and back humidity in polyester; lower body temperature in recovery in 4- and 6-channel shirts; no performance difference |
| Davis et al., 2017 |
8 male athletes, 45 min run, 32 °C |
No effect on core or skin temperature; lower chest microenvironment temperature in synthetic |
| De Alcantara Borba et al., 2016 |
6 men and 6 women, 10 km outdoor runs |
Pace unaffected by fabric or colour; Physiological Strain Index higher in cotton |
| Masoud et al., 2023 |
7 men with obesity, 30 min walk, 27 °C |
No superiority of polyester or cotton |
| Brazaitis et al., 2010 |
8 men, repeated bouts, 25 °C and 60% humidity |
Less sweat retained and faster skin temperature recovery in polyester |
| De Sousa et al., 2014 |
10 men, 45 min, 33 °C |
Polyester and elastane shirt retained less sweat; rectal temperature lower late in exercise |
| Raccuglia et al., 2018 |
Exercise study, participants not stated in abstract |
Higher fabric saturation went with a stickier feel; perceived wetness did not change between fabrics with different saturation, contact area and sweat content |
| Wang et al., 2014 |
Sweating torso manikin |
Thin fabrics keep evaporative cooling efficiency better |
| Teyeme et al., 2020 |
Four elastic knitted fabrics |
Polyamide and elastane knit combined short drying time with good airflow |
What this means when choosing
None of the studies above is a shopping guide, but together they suggest some sensible habits.
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Do not expect a performance edge. The trials mostly found no change in heart rate, core temperature, pace or main comfort scores. None of the abstracts summarised here reports whether quick dry fabric changes stickiness; Raccuglia et al. (2018) found only that stickiness tracked how saturated a fabric was.
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Fabric thickness is one thing researchers measure. In one manikin study, thin fabrics kept evaporative cooling efficiency better in tight-fitting sportswear (Wang et al., 2014), and a correlation analysis found yarn linear density, hairiness and fabric weight had the largest influence on heat resistance (Salopek Čubrić et al., 2022). Neither study tested shorts or says what suits a given session.
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Read the label. Quick dry and four-way stretch are descriptions. Check the garment label for its fibre content. If a listing does not give a fibre breakdown, a weight or a size chart, ask the seller.
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Conditions matter. In one small study of 12 men cycling at 15 °C, a wool shirt kept torso skin temperature higher than cotton, viscose or polyester after exercise in a windy chamber (Abedin and DenHartog, 2024); that does not apply to shorts or warm rooms.
Limits of the evidence
It is worth being plain about how little is settled.
- Almost every wearer trial used T-shirts. None of the studies summarised here tested gym shorts on their own, or pocket design, shorts length or squat range of motion with a stretch fabric. Of the abstracts we reviewed, only Gavin et al. (2001) states that participants wore shorts (cycling shorts, as part of a matching ensemble), and it did not test them separately.
- Most trials were small (7 to 12 participants), mainly men, mostly at 25 to 33 °C (one at 15 °C). There is little on women, on indoor lifting sessions or on very hot, humid conditions, which the 2022 review specifically asked for.
- The one fit study used work trousers in lifting tasks, and it measured low-back discomfort, so it should not be stretched to gym shorts.
- Teyeme et al. (2020) and the wicking and immersion tests in Dai et al. (2008) measured fabric samples; Dai et al. also ran wear trials with T-shirts. None of the abstracts we reviewed tested a finished garment with seams, panels, pockets and a waistband, so these results may not carry over to one.
- None of the studies summarised here tested how washing or ageing changes quick dry performance, so care advice rests on what a maker says.
- Some of the gains reported, such as lower sweat retention or humidity, were measured against cotton. Modern blends and knits vary widely, so a comparison with cotton says little about a given pair of shorts.
The Free Muscle product in this context
The Free Muscle Gym Shorts product page describes lightweight training shorts in sizes XS to XL. The page calls the fabric quick-dry and four-way stretch, and says it is intended for squatting, sprinting and stretching. In its own words the sweat-wicking fabric dries fast, and the four-way stretch is there so that deep squats and lunges do not feel restricted. These are the brand's descriptions, and the studies above do not test this garment.
Other details from the page, stated as the brand gives them:
- An elastic waist with drawcord, and fit advice to order your usual size.
- Zip side pockets meant to keep a phone and keys in place.
- A mid length described as suited to lifting, running and everyday wear.
- Reinforced seams.
- Care instructions to machine wash cold and hang to dry.
The page does not state the fibre composition, fabric weight, exact length, a size chart or a UPF rating. In line with the reading advice above, check the label on delivery and use the contact details on the site if you need a measurement before buying. Browse the wider Free Muscle merchandise collection for other apparel.
Frequently asked questions
What is quick dry fabric?
On the Free Muscle page quick dry is a description, and no drying time is given. In the research literature, Chang and Wang (2023) review the advanced technologies developed for quick-dry function in sportswear, and Teyeme et al. (2020) measured drying time directly as one of several fabric properties. The studies here did not test the Free Muscle garment.
What did wearer trials actually measure about quick dry fabric?
They measured core and skin temperature, heart rate, performance, sweat held in the garment, humidity against the torso and comfort ratings. In most trials with polyester and cotton, core temperature, heart rate and performance were similar, and the differences that did appear were mostly about moisture. The studies did not test the Free Muscle garment.
Does quick dry fabric keep you cooler?
Not reliably. Most trials with polyester and cotton found no difference in core or skin temperature in moderate heat. One 45-minute trial at 33 °C reported a lower rectal temperature late in the session for a polyester and elastane shirt, but it involved ten men (De Sousa et al., 2014).
Is quick dry polyester better than cotton for the gym?
The studies do not declare a winner on performance. In some trials polyester shirts held less sweat and showed lower humidity at the chest and back, but in Sperlich et al. (2013) the clothing wetness sensation did not differ, and Brazaitis et al. (2010) reported similar subjective sensations during exercise; comfort ratings were mostly the same. The fibre label and your own comfort are the practical checks.
What does four-way stretch mean?
Free Muscle describes its four-way stretch as moving in every direction. The term does not say how much stretch there is or what the fibres are; the fibre content on the label shows the fibres, and only a measurement or the maker can say how far the fabric stretches.
How can I check what my shorts are made of?
Read the care and composition label on the garment. If a product page does not list the fibre content, ask the seller before you buy.
Do sweat-wicking shorts reduce smell?
The review's abstract says sweat-soaked sportswear can become a breeding ground for the skin microbiome, a source of odour, and discusses textile materials, antibacterial treatments and adsorbent materials for odour control. It does not say that quick-dry fabric on its own reduces smell, and nothing here tests these shorts (Chang and Wang, 2023).
Why do some quick dry shorts still feel sticky?
In one exercise study whose abstract does not describe the participants, stickiness tracked how saturated the fabric was with sweat more than how much sweat there was in total (Raccuglia et al., 2018).
Does fabric thickness matter for hot workouts?
In manikin tests of tight-fitting sportswear, thinner fabrics kept evaporative cooling efficiency up better than a thick merino (Wang et al., 2014). The result applies to tight-fitting, single-layer sportswear tested on a manikin; the study did not test shorts or looser garments, and it does not say what suits a given session.
Do stretch shorts help with squats?
None of the studies summarised here tests that. The only fit study used work trousers, and its link to gym movement is weak (Eungpinichpong et al., 2013). Try a garment through your own range of movement and judge by feel.
How should I wash quick dry shorts?
Follow the care label. For the Free Muscle shorts, the product page says to machine wash cold and hang to dry. See the Free Muscle Gym Shorts product page for the care instructions.
Do dark colours make shorts hotter?
In a 10 km running study of T-shirts, colour did not change pace, heart rate, rectal or skin temperature, although the black cotton shirt itself reached a higher temperature and the Physiological Strain Index was higher in both cotton conditions (De Alcantara Borba et al., 2016). Colour was not tested in shorts.
Published by Free Muscle, which sells the product discussed in this article. This article is general information about textile research and is not medical advice. Free Muscle also sells research compounds for laboratory research use only, to customers aged 18 or over; they are not discussed here. They are not medicines or food supplements and not for human consumption. UK delivery is free and tracked, in plain packaging, and standard UK delivery takes 2 to 5 working days (delivery details). Unopened items in their original packaging can be returned within 30 days (returns information); for apparel returns see the refund policy.
Sources
- Di Domenico I, Hoffmann SM, Collins PK. The Role of Sports Clothing in Thermoregulation, Comfort, and Performance During Exercise in the Heat: A Narrative Review. Sports Med Open. 2022;8(1):58. doi:10.1186/s40798-022-00449-4 PMID 35482166
- Raccuglia M, Sales B, Heyde C, Havenith G, Hodder S. Clothing comfort during physical exercise - Determining the critical factors. Appl Ergon. 2018;73:33-41. doi:10.1016/j.apergo.2018.05.014 PMID 30098640
- Wang F, Annaheim S, Morrissey M, Rossi RM. Real evaporative cooling efficiency of one-layer tight-fitting sportswear in a hot environment. Scand J Med Sci Sports. 2014;24(3):e129-39. doi:10.1111/sms.12117 PMID 24033668
- Gavin TP, Babington JP, Harms CA, Ardelt ME, Tanner DA, Stager JM. Clothing fabric does not affect thermoregulation during exercise in moderate heat. Med Sci Sports Exerc. 2001;33(12):2124-30. doi:10.1097/00005768-200112000-00023 PMID 11740309
- Masoud AA, Alansare AB, Finch AE. Physiological effects of exercise in heat while wearing a polyester versus cotton T-shirt in physically active men with obesity: a pilot study. J Sports Med Phys Fitness. 2023;63(12):1358-1365. doi:10.23736/S0022-4707.23.15164-4 PMID 37721720
- Sperlich B, Born DP, Lefter MD, Holmberg HC. Exercising in a hot environment: which T-shirt to wear? Wilderness Environ Med. 2013;24(3):211-20. doi:10.1016/j.wem.2013.04.005 PMID 23870763
- Davis JK, Laurent CM, Allen KE, Zhang Y, Stolworthy NI, Welch TR, Nevett ME. Influence of Clothing on Thermoregulation and Comfort During Exercise in the Heat. J Strength Cond Res. 2017;31(12):3435-3443. doi:10.1519/JSC.0000000000001754 PMID 27984496
- De Alcantara Borba D, Ferreira JB, Coelho LG, Martini AR, Lgonçalves Madeira L, Coelho DB, Prado LS, Bemben MG, Rodrigues LO. T-Shirt fabric and color affect the physiological strain but not 10 km outdoor running performance. J Sports Med Phys Fitness. 2016;56(4):359-67. PMID 25567048
- Brazaitis M, Kamandulis S, Skurvydas A, Daniusevičiūtė L. The effect of two kinds of T-shirts on physiological and psychological thermal responses during exercise and recovery. Appl Ergon. 2010;42(1):46-51. doi:10.1016/j.apergo.2010.04.001 PMID 20427033
- De Sousa J, Cheatham C, Wittbrodt M. The effects of a moisture-wicking fabric shirt on the physiological and perceptual responses during acute exercise in the heat. Appl Ergon. 2014;45(6):1447-53. doi:10.1016/j.apergo.2014.04.006 PMID 24768089
- Abedin F, DenHartog E. Clothing impact on post-exercise comfort: skin-clothing physiology in transient environment. Ergonomics. 2024;67(8):1080-1096. doi:10.1080/00140139.2023.2281272 PMID 37960939
- Dai XQ, Imamura R, Liu GL, Zhou FP. Effect of moisture transport on microclimate under T-shirts. Eur J Appl Physiol. 2008;104(2):337-40. doi:10.1007/s00421-007-0628-z PMID 18071744
- Chang Y, Wang X. Sweat and odor in sportswear - A review. iScience. 2023;26(7):107067. doi:10.1016/j.isci.2023.107067 PMID 37534139
- Aguilera J, Navarrete-de Gálvez E, Sánchez-Roldán C, Herrera-Ceballos E, de Gálvez MV. Sun-protective Properties of Technical Sportswear Fabrics 100% Polyester: The Influence of Moisture and Sweat on Protection against Different Biological Effects of Ultraviolet (UV) Radiation. Photochem Photobiol. 2023;99(1):184-192. doi:10.1111/php.13679 PMID 35877464
- Teyeme Y, Malengier B, Tesfaye T, Vasile S, Van Langenhove L. Comparative Analysis of Thermophysiological Comfort-Related Properties of Elastic Knitted Fabrics for Cycling Sportswear. Materials (Basel). 2020;13(18). doi:10.3390/ma13184024 PMID 32927922
- Salopek Čubrić I, Potočić Matković VM, Pavlović Ž, Pavko Čuden A. Material and Structural Functionalization of Knitted Fabrics for Sportswear. Materials (Basel). 2022;15(9). doi:10.3390/ma15093306 PMID 35591640
- Eungpinichpong W, Buttagat V, Areeudomwong P, Pramodhyakul N, Swangnetr M, Kaber D, Puntumetakul R. Effects of restrictive clothing on lumbar range of motion and trunk muscle activity in young adult worker manual material handling. Appl Ergon. 2013;44(6):1024-32. doi:10.1016/j.apergo.2013.04.002 PMID 23642759
