Interest in testicular cooling has grown among men trying to conceive, patients preparing for assisted reproduction, individuals exposed to occupational or lifestyle heat, and those interested in protecting their reproductive health.

The biological rationale is straightforward: sperm production requires the testes to remain cooler than core body temperature, and prolonged heat exposure has been associated with temporary changes in semen quality in both experimental and observational studies.

Several commercial testicular cooling products are now available, but they differ substantially in how they work, how long they cool and the quality of evidence supporting them.

Cooling is not a treatment for every cause of male infertility. Genetic, hormonal, anatomical, inflammatory and lifestyle factors may all contribute to impaired fertility. Cooling should therefore be viewed as one possible temperature-management strategy rather than a substitute for medical evaluation.

This article compares the main categories of testicular cooling—from breathable underwear and frozen inserts to wearable active cooling systems. Rather than identifying a single "best" solution, it explains how these approaches differ, their practical advantages and limitations, and what current scientific evidence actually supports.

Why temperature matters

Human spermatogenesis requires the testes to remain cooler than core body temperature. This is achieved through several natural thermoregulatory mechanisms, including the position of the testes outside the body, heat exchange within the spermatic cord and changes in the distance between the testes and the body.

Everyday factors such as prolonged sitting, heated car seats, tight clothing, fever, saunas and high ambient temperatures can challenge these mechanisms and increase scrotal temperature. Experimental and observational studies have associated prolonged genital heat exposure with temporary deterioration in semen quality.

A lower scrotal temperature alone does not guarantee improved fertility. Temperature is only one factor among many—including genetics, hormones, anatomy and lifestyle—that influence male reproductive health.

Research Spotlight

Dr Andreas Jung is one of the pioneers in research on scrotal temperature and male fertility.

His studies demonstrated that prolonged genital heat exposure may impair semen quality and that nocturnal scrotal cooling may improve semen parameters in selected patients.

He also investigated the effects of heated car seats and everyday heat exposure, helping establish the biological rationale for testicular cooling.

However, most published studies were relatively small and involved selected patient groups. Larger, well-controlled randomized clinical trials are still needed to determine whether cooling translates into meaningful improvements in fertility outcomes such as pregnancy and live birth rates.

How to compare cooling methods fairly

Comparing cooling methods requires more than simply looking at reported temperature reductions. A fair comparison should consider:

• Measured location: scrotal skin temperature is not identical to intratesticular temperature.
• Baseline conditions: sitting, walking, room temperature and clothing can substantially change results.
• Cooling profile: a short strong temperature drop is different from a smaller sustained reduction.
• Daily adherence: a theoretically effective device has little value if it is uncomfortable or impractical.
• Clinical endpoints: temperature change, semen parameters, pregnancy and live birth are different outcomes.
  

Testicular cooling methods range from simple changes in clothing to frozen inserts and powered wearable systems. Passive structural methods prioritise simplicity and continuous wear but may provide modest, environment-dependent cooling. Frozen-pack devices can produce more direct cooling but require preparation and repeated replacement. Active systems can remove heat continuously while powered, but they are more complex.

Passive cooling and active cooling

Passive methods do not use a powered heat-removal system. They either reduce heat retention, improve airflow, separate the scrotum from the thighs, or absorb heat through a pre-cooled material. Passive cooling can be divided into two practical groups:

Structural passive cooling: breathable or anatomically shaped underwear, looser clothing and designs that lift or separate the scrotum.

Stored-cold passive cooling: ice packs, gel packs or phase-change inserts that absorb heat until they warm toward body temperature.

The advantages are simplicity, low weight, silence and no need for power. The disadvantages depend on the design. Airflow-based underwear may provide only modest cooling, while frozen or chilled inserts lose their effect over time and must be re-cooled or replaced. Temperature can also vary during a session as the insert warms.

Active systems use energy to move heat away from the body. A wearable active system may combine a thermoelectric element, a heat exchanger, a circulating fluid path, fans and electronic control. Unlike a frozen insert, an active system can in principle continue removing heat while power is available.

Unlike passive cooling methods that rely on stored cold, active cooling systems are designed to remove heat continuously while power is available. This allows a more stable and controlled cooling profile without the progressive warming that naturally occurs as ice or gel packs approach body temperature.

Because spermatogenesis is a continuous biological process lasting approximately 74 days, maintaining favourable thermal conditions over extended periods may be more physiologically relevant than occasional short cooling sessions.

Airflow-based and anatomical underwear

The least intensive approach is to reduce insulation and compression. Conventional recommendations often include avoiding excessive heat exposure and, where comfortable, choosing looser or more breathable clothing. Purpose-designed underwear attempts to go further by supporting the testes away from the thighs or using mesh to improve ventilation.

Cool Beans is an example of this structural passive category. The manufacturer describes a pouch that lifts the scrotum forward and uses airflow rather than frozen inserts. This may be attractive for men who want a device-free daily garment. Its practical limitation is that it does not actively remove heat: the resulting temperature depends on ambient conditions, activity, outer clothing, anatomy and posture.

This approach primarily supports the body's natural thermoregulation rather than actively removing heat.

Cooling underwear with frozen or chilled inserts

Cooling underwear combines a wearable garment with a pocket for a cold insert. Snowballs is a prominent example. According to the manufacturer, its gel packs are frozen before use and provide approximately 30 minutes of cooling per insert.

A 2021 crossover study monitored scrotal skin temperature during cyclic cooling with SnowWedge inserts. Median temperature was lower during the cooling period than during the control period. This shows that the device can temporarily change scrotal skin temperature under the study conditions. It does not, by itself, establish an improvement in pregnancy rates or prove superiority over other methods.

This approach offers stronger immediate cooling than airflow-only underwear, but it requires planning. Users need freezer access, multiple inserts for repeated sessions, and a routine for exchanging packs. The cooling intensity also changes continuously as the insert warms.

Seated cooling devices

Some devices focus specifically on the heat generated by sitting. The Underdog uses a frozen, insulated wedge placed between the seat and the user's clothing. This format is intended for desk work or driving and avoids placing a pack directly inside underwear.

Its strength is task-specificity: sitting is a well-documented contributor to rising scrotal temperature, and the device is designed around that scenario. Its limitation is the same specialization. It is less suited to walking or general all-day mobility, and it still depends on pre-freezing and finite stored cold.

The manufacturer reports temperature reductions in small tests, but independent, peer-reviewed evidence on semen, pregnancy or live-birth outcomes is limited.

Conventional ice and gel packs

Older clinical studies often used relatively simple cooling arrangements, including ice packs held in place at night. Some reported improvements in sperm density or motility, but the studies were generally small and methodologically heterogeneous.

A conventional pack is inexpensive, but it is not necessarily equivalent to a purpose-designed device. Direct contact with very cold material can cause discomfort or cold injury. Cooling should be insulated, tolerable and stopped if pain, numbness, marked skin colour change or persistent discomfort occurs. Men with reduced sensation, vascular disease, skin disorders or recent surgery should seek medical advice before local cooling.

Active wearable cooling

Active wearable cooling uses an engineering approach fundamentally different from passive methods. Instead of relying on stored cold, it continuously transfers heat away from the body while power is available. CoolMen is an example of a wearable active cooling system that combines a cooling pad with an external belt-mounted thermoelectric module powered via USB-C.

The potential advantage is continuity: the user does not need to exchange warming gel packs while the system remains powered. Active cooling may also allow closer control of operating conditions than a melting or warming insert. These are engineering advantages, not proof of a fertility benefit.

Active systems also introduce new considerations: battery life, noise, weight, cleaning, fluid or thermal-system integrity, electronic safety, skin-contact temperature and correct use. Independent comparative trials are needed to determine whether sustained active cooling produces clinically meaningful advantages over simpler passive methods.

Conclusion

The science supports taking genital heat exposure seriously, particularly in men with fertility concerns. It also supports caution: the current evidence base is too limited to label any product as universally best or to promise improved conception. The most scientifically sound approach is to compare mechanisms honestly, measure real-world usability, distinguish temperature effects from fertility outcomes and place cooling within a broader medical evaluation. 

References

1. Jung A, Schuppe HC. Influence of genital heat stress on semen quality in humans. Andrologia. 2007;39(6):203-215. PubMed PMID: 18076419.
2. Jung A, Leonhardt F, Schill WB, Schuppe HC. Influence of heating car seats on scrotal temperature. Fertility and Sterility. 2008;90(1):335-339. PubMed PMID: 17919605.
3. Jung A, Eberl M, Schill WB. Improvement of semen quality by nocturnal scrotal cooling and moderate behavioural change to reduce genital heat stress in men with oligoasthenoteratozoospermia. Reproduction. 2001. PubMed PMID: 11277880.
4. Jung A, Schill WB, Schuppe HC. Improvement of semen quality by nocturnal scrotal cooling in oligozoospermic men with a history of testicular maldescent. International Journal of Andrology. 2005. PubMed PMID: 15811070.
5. Nikolopoulos I, Osman W, Haoula Z, Jayaprakasan K, Atiomo W. Scrotal cooling and its benefits to male fertility: a systematic review. Journal of Obstetrics and Gynaecology. 2013;33(4):338-342. PubMed PMID: 23654310.
6. Garolla A, Torino M, Sartini B, et al. Seminal and molecular evidence that sauna exposure affects human spermatogenesis. Human Reproduction. 2013;28(4):877-885. PubMed PMID: 23411620.
7. Bujan L, Daudin M, Charlet JP, et al. Increase in scrotal temperature in car drivers. Human Reproduction. 2000;15(6):1355-1357. PubMed PMID: 10831568.
8. Zumstein V, Betschart P, Vetterlein MW, et al. Stay cool! Special underwear for cyclic cooling significantly decreases scrotal skin temperature. Urologia Internationalis. 2021. PubMed PMID: 34729240.
9. Osman MW, El-Sharkawy MA, Awadalla A, et al. A study of the effect of the FertilMate scrotum cooling patch on male fertility. Human Fertility. 2012. PubMed PMID: 22540417.
10. Thonneau P, Bujan L, Multigner L, Mieusset R. Occupational heat exposure and male fertility: a review. Human Reproduction. 1998;13(8):2122-2125. PubMed PMID: 9756281.
11. Snowballs Underwear. Product and 'How It Works' pages. Manufacturer information accessed July 2026.
12. Underdog Fertility. Product and 'How The Underdog Works' pages. Manufacturer information accessed July 2026.
13. Cool Beans Underwear. Product, fertility and technology pages. Manufacturer information accessed July 2026.

Medical disclaimer
This article is intended for educational purposes only and does not constitute medical advice. Male infertility has many potential causes, and persistent fertility concerns should always be evaluated by a qualified healthcare professional. Mention of commercial products does not constitute endorsement.

Trademark notice
Product names, trademarks and registered trademarks mentioned in this article are the property of their respective owners and are used solely for identification and comparison purposes.