Rubber Chronicle 21: Yulex Wetsuits Keep You Warmer

May 30, 2024


Rubber Chronicles

GUL Wetsuit closeup - Made with YULEX

Scotland is surrounded by Atlantic and North Sea swells and guarantees some great waves, along with golden sandy beaches, long coastlines, and beautiful clear water, leading it to be one of Europe's top surfing destinations and a great alternative to the crowded breaks of southern Europe. 

So, when we were informed by GUL that their Yulex natural rubber foam wetsuit out-performed other comparable petroleum-based neoprene wetsuits for the Lost Shore Surf Resort testing, we were immediately stoked. Lost Shore Surf Resort is a Wavegarden powered inland wave pool in Edinburgh, Scotland opening in September 2024. Then, my second immediate thought was “dreich [dreekh]” because Scotland ocean waters are cold. The average temperature ranges from 5–8°C (41–46°F) in February to 12–16°C (54–61°F) in August. 

Yulex did not sponsor the testing. We have never collaborated with any of the Lost Shore staff. We were not asked for our opinion or advise before or during the testing period, nor did we influence the wetsuit brands that were evaluated or the testing method. All these activities occurred before we were told of the results. Once we were informed of the project, our interests peaked, and we visited Lost Shore in January of this year. The weather was about +48F, winds were about 18 mph, and humidity was 84%. Dreich. 

The Lost Shore team are an enthusiastic and passionate group of people- namely, Andy Hadden, Mark Stewart, Alejandro Padro, and Scott Mitchell. To perform the tests, the Surf Lab was formed which is a partnership between the School of Applied Sciences at Edinburgh Napier University and Lost Shore Surf Resort. Brendon Ferrier, who has a Ph.D. in Performance Analysis & Biomechanics, is the lead for the Surf Lab and the Head of Performance Support for the Scottish Surfing Federation. 

GUL’s Yulex wetsuit is made from Yulex’ new supply chain in Southeast Asia. Based on the Yulex formulation and resulting physical properties of the foam, we know it is a high-quality product, but still it is good to see it evaluated and compared to neoprene wetsuits from other major brands and performing well (and better).

Surf Lab Testing of Wetsuits for Selection of Lost Shore Surf Resort Wetsuit Fleet

We reviewed the Surf Lab data and where appropriate refer to other relevant studies on wetsuit thermoregulation. The complete references and detailed methods are described at the end. 

Summary of the test methods used to select the Lost Shore rental fleet wetsuit: 

  • 9 brands were invited to submit their wetsuit for testing and the brand wetsuit that overall provided the best warmth and comfort under the tested conditions was selected. 
  • All wetsuits have nylon laminated on the interior and exterior sides of the closed-cell foam. No wetsuits had internal thermal linings or exterior smooth skin. 
  • All wetsuits are 5/4 mm or 5/3 mm wetsuits and tested with the brand’s accessories (booties and gloves). 
  • All wetsuits have GBS seams and taped construction at critical entry points. 
  • All wetsuits except one (Wetsuit E, Yulex foam) are neoprene-based wetsuits. 
  • All wetsuits have a back zip. 
  • No accessories (booties and gloves) had cuffs. 
  • The adult male test subject is a surfer and did not wear additional garments or layers underneath the wetsuits.
  • The same test subject was used for all tests. 
  • Each 30-minute test run started with the same water and body temperature conditions; and temperatures were taken at the bottom and top of the ice bath to ensure 10C temperatures were maintained.
  • 8 body regions were monitored using wireless thermal sensors for the measurement of skin temperature, and four readings were taken every minute for 30 minutes.
  • This is a static test in a 10C ice water bath recovery pod. 
  • Only body temperatures from the 8 thermal sensors were collected. 
  • Table 1 describes the Wetsuits A-E tested.
  • Table 2 describes the average body temperatures for Wetsuits A-E. 
  • Table 3 describes the temperature for each body region from the baseline temperature. 

Table 2:  Average Body Temperature for Wetsuits A-E
Table 3: Temperature Drop for Each Body Region from the Baseline Temperature


Lost Shore called for submissions of wetsuits from 9 brands and whittled them down to 5 brands to be tested. The Surf Lab was then asked to test the 5 wetsuit brands chosen, to provide some evidence for Lost Shore to objectively select the best wetsuit fleet for the surf resort.  Lost Shore did not otherwise influence the testing, the methods used or results, which was all performed at the Surf Lab at Edinburgh Napier University. Surf Lab alone was responsible for the test methods, design, controls, data, and analysis.

All wetsuits tested have a similar composition: back zips; nylon interior and exterior fabrics; GBS seams; 5mm for body core; 3-4mm for the arms and legs (except Wetsuit B); 5mm for booties (except Wetsuit E); and 3mm for gloves (except Wetsuit E). See Table 1.

Average body temperatures were monitored and recorded from 8 body regions: Abdomen, Chest, Lower Leg, Upper Leg, Forearm, Upper Arm, and Upper Back Lower Back. See Table 2. Over a 30-minute immersion, the subject in Wetsuit E maintained the highest average body temperature. In other words, when taken as a whole, Wetsuit E kept the subject’s body temperature the warmest.

Total body temperature drop was also recorded, with Wetsuit D having the best, or least temperature drop, and Wetsuit E being the second best. See Table 3.


To maintain stable internal body temperatures (homeostasis), our body is constantly balancing heat loss and heat gain– we thermoregulate. Moreso, humans can detect temperature changes as small as 0.003°C 1.

What makes thermoregulation critical for water sports, particularly surfing, is that the rate we transfer heat to water is 25% greater than what we transfer to air. Stated another way, our heat loss to water is 3–5 times greater than our heat lost to air2. This is especially important if surfing in cold waters is your jam because it means that you are losing massive amounts of your body heat to the water. 

To illustrate this in another way, heat moves along a gradient from high to low. Take warm bodies in icy water, there is only one direction for that body heat to go– it gets lost to the water. Hence, body heat loss is challenging for extended periods of time. To reduce this loss for surfers, the closed-cell construction of wetsuit foam, whether it is Yulex foam or neoprene/geoprene foam, aids to trap heat in those cells, and that trapped heat also helps to warm the thin layer of water surrounding the body underneath the wetsuit. And all this helps surfers maintain better body temperatures, enabling surfing in cold water environments like Scotland or anywhere where water temperature is significantly lower than body temperature (97-99°F or 36-37°C). 

Studies have shown that different regions of the body have different skin temperatures, with and without wetsuits 3,4, and in static or dynamic cold-water conditions e.g. surfing 5, 6, 7, 8.  Surf Lab’s testing is consistent with the results of these previous studies under static cold-water conditions. Thus, an assumption can be made that Surf Lab’s results in static water conditions would also be true in surf water environments. 

Interestingly, however, a recent study published in 2023 showed that changes in skin temperature did not always align with the surfer’s own perception and/or their response to their changing body temperatures. This study asked 903 surfers, male and female, ages 18-80, wearing full wetsuits of any thickness while surfing with no limitation on time, with or without booties and gloves, along the northern, central, and southern California coast (different ocean temperatures), to complete a post-surf survey of questions relating to their perceived thermal comfort or thermal perception9. The take home of this study in view of prior studies is a surfers’ perception of heat loss (subjective) will always be a factor in staying warm in the water. 

The test results from the Surf Lab study shows that the subject’s abdomen and chest (or core) regions were the best at retaining heat, which is expected and a normal body reaction. Blood flow is reduced to the arms, legs and skin and maintained at the core to protect our vital organs and help fight against hypothermia. This study also showed that the loss of body heat in all the other body regions was also greater than that of the abdomen and chest. Previous studies showed that the legs lose more body heat to the water because of the constant seawater movement over them e.g. paddling 9,10. The reduction of blood flow to arms and legs of course also makes catching waves a challenge in very cold water.

The greatest body temperature drop was that in the lower back region, with the subject in Wetsuit B and C, dropping average body temperatures of 15°C (37°C to 22°C). When determining the root cause of the significant heat loss in the lower back, it was observed that the zippers and seams were porous and cold water was continuously moving through the wetsuit, aka “flushing.” To reduce flushing into the back regions, GUL (Wetsuit made with Yulex foam) improved both the zipper and the zipper seams. This change was done after the testing in Tables 1-3. The Lost Shore wetsuit fleet will be GUL Yulex foam suits with the improved zipper and seam designs, potentially improving upon the results we see for wetsuit E. This design change should permit longer and more comfortable surf sessions at Lost Shore Resort.

In general, this study showed that body heat loss in 10C water (4.50C to 15.50C temperature drop, Table 3) is significantly greater than the body heat loss reported by surfers in Southern California (about 6.50C) where average water temperatures are 160C 7. Therefore, the colder the water, the more heat loss there will be to the water and the critical role that a warm wetsuit will play. 


No wetsuit was able to maintain normal body temperature (97-99°F or 36-37°C) when exposed to 10C water for 30 minutes. Surfers need a wetsuit. But the wetsuit that performed the best of the ones that were evaluated was Wetsuit E, which turns out was from GUL, a UK-based company that has been making wetsuits since 1967 in Newquay, Cornwall. GUL's wetsuit range include both summer and winter suits, as well as drysuits, and soon wetsuits made from Yulex foam. 

Lost Shore Surf Resort (“LSSR”)

About Lost Shore Surf Resort

Lost Shore Surf Resort (“LSSR”) is re-purposing an abandoned industrial quarry into a publicly accessible Country Park with a Wavegarden Cove. The proposed change will create natural capital value developing less than 50% of the 60-acre site. The water will be sourced from the nearby Union Canal (not competing for potable or drinking water) and cleaning it.  LSSR will consume about 30,000 – 50,000 cubic meters of water a year, which is about the same as a football stadium or Olympic size swimming pool, but 2-3x less than an 18-hole golf course. Wavegarden cove technology uses 10x less energy than the pneumatic systems that some of the other wave pool technologies offer. LSSR will also use a Green Energy Tariffs that pay for the cost of generating power from renewable -sources- for example, solar and wind power generation does not emit greenhouse gases, unlike the burning of fossil fuels for generation electricity.


  1. Fillingeri D, Morris NB, Jay O (2016) Warm hands, cold heart: progressive whole-body cooling increases warm thermosensitivity of human hands and feet in a dose-dependent fashion. Exp Psychol 102(1):100–112.
  2. Nimmo M (2004) Exercise in the cold. J Sports Sci 22(10):898–915.
  3. Riera, F., R. Hoyt, X. Xu, B. Melin, J. Regnard, and L. Bourdon. 2014. “Thermal and Metabolic Responses of Military Divers during a 6-H Static Dive in Cold Water.” Aviation, Sport, and Environmental Medicine 85 (4): 1–9.
  4. Tikuisis, P. 2003. “Heat Balance Precedes Stabilization of Body Temperatures during Cold Water Immersion.” Journal of Applied Physiology 95: 89–96.
  5. Hayward, J. S., M. Collis, and J. D. Eckerson. 1973. “Thermographic Evaluation of Relative Heat Loss Areas of Man during Cold Water Immersion.” Aerospace Medicine 44 (7): 708–711.
  6. McArdle, W. D., M. M. Toner, J. R. Magel, R. J. Spinal, and K. B. Pandolf. 1992. “Thermal Responses of Men and Women during Cold-water Immersion: Influence of Exercise Intensity.” European Journal of Applied Physiology and Occupational Physiology 65: 265–270.
  7. Corona, L.J., Simmons, G.H., Nessler, J.A., Newcomer, S.C., 2018. Characterization of regional skin temperatures in recreational surfers wearing a 2mm wetsuit. Ergonomics 61 (5), 729–735.
  8. Warner, Mackenzie, Jeff A. Nessler, Davide Filingeri, Sean C. Newcomer 2023, The characterization of thermal perception in recreational surfers wearing wetsuits, Applied Ergonomics 113: 104108
  9. Schilling, C. W. 1984. The Physician’s Guide to Diving Medicine. New York: Plenum Press. 
  10. Young, A. J., M. N. Sawka, and K. B. Pandolf. 1996. Nutritional Needs in Cold and in High-altitude Environments: Applications for Military Personnel in Field Operations, 127–147. Washington, DC: National Academies Press.

Testing Facilities and Resources

  1. The Surf Lab is a research collaboration between Edinburgh Napier University and Lost Shore Surf Resort; Contact: Brendon Ferrier (PhD), School of Applied Sciences, Edinburgh Napier University, Sighthill Campus, EH11 4BN Contact: Brendon Ferrier, Ph.D. 
  2. Dept. of Kinesiology at California State University, San Marcos, California, USA Contact: Jeff Nessler, Ph.D. and Sean Newcomer, Ph.D.
  3. The Center for Surf Research, San Diego State University, San Diego, California, USA. 
  4. Surf Flex Lab, Innovation Campus, Squires Way, Wollongong, New South Wales 2519, Australia 
  5. Thermosense Lab, Skin Sensing Research Group, University of Southampton, Clinical Academic Facility | South Academic Block, Southampton General Hospital I SO16 6YD, Southampton, UK Contact: Davide Filingeri, Ph.D. 

Detailed Methods

5 branded wetsuits were used for this study, with a single participant of 172 centimetres tall and weighing 64 kilograms. All testing was performed on the same day within a temperature-controlled environment ~170C and approximately 70% humidity.

Testing was performed in a Lumi recovery pod (Lumi, Exeter United Kingdom) measuring 75cm in height and 80cm in diameter, holding approximately 300 litres of cold water measured at 10C during each testing session. Water temperature was measured at the surface using a LUMI branded thermometer and at the bottom of the ice bath using a Testo infrared laser thermometer (Testo 830-T1, Testo, Philippines), with the emissivity setting set to the factory setting of 0.95. Water temperature was measured two times at the surface and at the bottom of the pool before immersion, with the water being stirred between measurements. Temperature was intermittently measured at the surface and at the bottom during the immersion period, and at the end of each immersion to ensure a consistent water temperature. If the water temperature was seen to rise above 1.50C, ice was added to the bath and stirred. 

To test the wetsuit performance eight i-buttons (DS1922L, were placed on the right side of the participant (mid-calf (between the medial and lateral heads of the gastrocnemius), mid-thigh (midway between the patella and the inguinal fold at the hip, on the anterior surface of the thigh), abdomen (5 centimetres lateral to the umbilicus), lower back (10 centimetres lateral to L5-S1 of the vertebral column), chest (at the junction of a line running downwards midway from the clavicle and laterally from the sternum ), upper back (centre of the scapula), upper arm (midway between the elbow and shoulder, placed on the belly of the triceps muscle), and forearm (midway between elbow and wrist, on muscle belly of the wrist flexors). Prior to the placement of the i-button sensors, each sensor was placed within a small ziplock bag to ensure waterproofing after each sensor was programmed using the OneWireViewer software to set the parameters of the data collection. Each sensor was set to capture data every 10 seconds during the testing period.

Prior to the placement of the sensors, and fitting of the wetsuit, temperatures of the participants right foot (top of foot), right hand (back of hand), and abdomen (just next to i-button placement) was taken using the Testo 830-T1 to ensure the temperature of the participant was at a similar magnitude at each testing session. The skin temperature was required to be at the initial recorded temperature of 240C (foot), 250C (hand) and 330C (abdomen) for a period of 3 minutes before re-submersion of the subsequent wetsuit model. 

Once ready for submersion, the participant was asked to step into the Lumi recovery pod and assume a comfortable seated position, with the water reaching a level in line with the top of their shoulder/upper trapezius musculature. The participant was asked to maintain this position, with the arms held loosely and legs folded for a period of 30 minutes. Periodically, the participant was asked to slowly move their arms in a swirling manner around the body for 30 seconds to stir and remove the thin boundary layer of warmer water. Ensuring the wetsuit and body were consistently affected by the temperature of the water. At the end of the 30 minutes of immersion, the participant was asked to exit the ice bath and remove the wetsuit to allow for the collection of the i-buttons and stopping of data collection and downloading of the data to be analysed. 

All data was then entered into a MS Excel spreadsheet and time synchronised from the sensor time stamp to allow for the alignment of the data and further analysis. Each wetsuit model was then compared at each anatomical site for performance measures across the eight body sites. 

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