How The Underdog Works

The Underdog is a patented non-invasive, low-risk cooling system designed to gently cool the scrotum and testicles to prevent sperm from overheating when sitting.

All you have to do is freeze it, sit, then slide The Underdog into position.


Ice Your Balls for Fertility with Underdog Cooling Device


The Underdog uses a wedge-shaped ice pack and precision double insulation system to do what normal ice packs can't: deliver a gentle and optimal level of cooling.

The Underdog should be used whenever driving or sitting for longer than 20 minutes.

Each pack lasts for 3 hours, and a spare pack is included so you’re never without cooling.

underdog family with baby in carriage

Why Use Cooling

Getting pregnant isn't always easy. And our offspring are the most important investment of our lives. Why not use everything at our disposal including The Underdog to optimize sperm quality, which is a key factor in getting pregnant, carrying to term (even with IVF), and having healthy outcomes. 

How to Optimize Male Fertility

When seeking to boost fertility, it's essential to maximize sperm quantity and optimize sperm quality.  This means following a healthy lifestyle: eating better, exercising, reducing stress, reducing smoking and alcohol, and making sure we're getting essential nutrients from food and possibly male fertility supplements. It also means keeping our testicles cool so they're at the optimal temperature for sperm production. 

Heat and Male Infertility

Male fertility has been plummeting in the western world. A 2017 meta-study concluded that sperm counts are down more than 50% in the past 40 years, with a continued decreasing trend. An estimated 15% of couples now face infertility challenges, with a male factor contributing half of the time.

While there are a number of possible factors for male sub-fertility and male infertility, scientific studies suggest a correlation between reduced viable sperm count and overheating due to sitting, driving, and obesity. 

In fact, the rise of the information economy has caused jobs requiring physical activity to drop from 50 percent in 1960 to just 20 percent today - a time frame which coincides with the decline in fertility. And a 2017 survey found individuals employed full time now spend an average of 12 hours sitting per day. Overheating from office jobs and commuting could be a root cause of reduced male fertility.


Infographic showing accumulated testicular heating while sitting.

Trying to Hang Out

The scrotum hangs outside the body for a very cool reason: sperm formation is extremely sensitive to testicular overheating. The optimal testicles temperature for sperm formation is 3 degrees C (5.4 degrees F) below body temperature.  

hot balls overheated testicles


But we overheat our testicles by sitting or driving for longer than 20 minutes, wearing our normal clothing, and underlying medical conditions like obesity or varicocele. These defeat our natural cooling systems, causing scrotal temperature to rise into the danger zone harmful to sperm production. 

Enter The Underdog

the underdog testicle cooling device ice pack and sleeve

The Underdog is a simple, non-invasive, low-risk cooling device that keeps the scrotum in an optimal temperature range by counteracting temperature rise from body-heat when sitting. It uses a gently contoured wedge-shaped ice pack that fits any body shape, and a soft sleeve with engineered thermal insulation. Once seated, the Underdog slips easily between the seat and pants. 

And best of all, no special clothes are required!

  • No bulging underwear
  • No wet pants
  • No discomfort
  • No overheating

 It's easy to make The Underdog a part of your daily routine.


underdog ice pack with keys, wallet, sunglasses

Quick Start

Using The Underdog is easy:

  1. Freeze both ice packs
  2. Sleeve an ice pack
  3. Insert The Underdog between seat and pants

See the Detailed User Guide for more detailed instructions.


The Ice Packs

The ice pack creates the perfect contoured wedge shape to adapt to every body shape and seating surface.  When sleeved, simply move it towards the body to make comfortable contact with the pants and scrotum.

The kit comes with 2 ice packs so you're never without cooling. 

Each ice pack lasts for 3-4 hours and will re-freeze in 2-3 hours in a standard freezer. 


The Sleeve

The sleeve uses a precisely engineered double-insulation technique for just the right amount of cooling. The sleeve is soft and comfortable, and the cooling effect is barely noticeable.  

A velcro closure system makes for easy swapping of ice packs.

The discreet, masculine black color nearly disappears when in use.

And importantly, the sleeve is impermeable to the water vapor that causes condensation. So you won't get wet pants or a wet chair.


When to Use The Underdog

Whenever sitting for longer than 20 minutes:

  • At the Office
  • Driving
  • Relaxing at Home


using underdog at the office

using the underdog while driving

using the underdog on the couch at home


How Does The Underdog Compare to Snowballs Cooling Underwear?

Precision Cooling

  • The Underdog's patented insulation provides gentle, controlled cooling of 2-3 deg. C for 3 hours to keep testicles in the optimal range (33-34 deg. C) for sperm production.
  • Snowballs provides extreme cooling for less than 30 minutes, then expires. In our probe experiment, Snowballs caused an extreme 15 deg. C scrotal temperature drop in one test subject. We question if this is effective or safe.

Comfort and Convenience

  • The Underdog is very comfortable, non-intrusive, and can be easily put aside when it's time to get up and move.  
  • Snowballs Underwear requires wearing bulky ice packs inside special underwear. This is uncomfortable, inconvenient, requires frequent trips to the washroom to swap ice packs, and may cause a bulge in the pants.

 the underdog ice wedge and sleeve


Download User Guides

Buy The Underdog on Amazon


he Underdog is protected by US Patent No. US11,540,939, and international patents pending.

Underdog, The Underdog, Underdog Fertility and the dog face logo are trademarks of Underdog Fertility and protected by US registered trademark No. 5,833,529.

The Underdog product is a general wellness device, and is not intended for use in the the cure, mitigation, treatment, or prevention of underlying disease or medical conditions.