Avoid both! Both briefs and boxer-briefs trap lots of heat! They are very bad for your testicles. You do Not want both compression and over-heating. Think about it: You compress and prevent your testicles from dropping to cool--and then you also overheat them? That's a recipe for cooked balls.
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​Conclusion: Avoid supportive underwear that has poor heat ventilation. Unless you want  testicular damage.

Supporters and jockstraps are the worst! Not only do they typically trap a lot of heat, but they also typically over-compress the testicles. You really cannot find a good compression supporter because they all squish your testicles and penis together into a ball! Someone really didn't understand why your testicles are outside of your body when they designed these things.

Conclusion: Avoid both supporters and jockstraps whenever possible, unless you want impaired testosterone and fertility. 

Boxers seem like a good option at first... I mean, they are more breathable right? Well, no, boxers trap just as much heat as briefs, because they typically have much more fabric! I have yet to find any boxers that are good at ventilating heat, and believe me, I've search through dozens of brands! Moreover, boxers allow scrotal sagging--which does not look good, and is unhealthy in the long run.

Conclusion: Boxers seem like a good option at first, but they are Not. Try to avoid boxers unless you want testicular overheating and scrotal sagging (which is unhealthy in the long-run).

Going commando is probably the best option so far. I mean why are our balls--the one body part that needs to be kept cool, wrapped up in multiple layers of clothes? It's irrational--an irrational social norm. Even though going underwearless  is the best option for keeping your testicles cool, it still doesn't provide scrotal support.

Conclusion: Likely, by far the best option here--much better than briefs, supporters, and boxers. Going commando is a good option.

The best cooling underwear is one has a specially designed fabric, separates the penis and the balls, all at the same time providing light support for the testicles--improving blood circulation and not over-heating the testicles.

Conclusion: Buy the STUD Underwear it is the best cooling & testicular support underwear. It is great for varicocele.

5 Reasons to use Stud Briefs for varicocele natural treatment: Cooling, seperation, surgery-free solution, discreet varicocele treatment, and improved circulation.

Briefs, Boxer Briefs, & Jockstraps: Squish penis and testicles into a ball and trap lots of heat. Trapped heat damages the testicles, and causes both pain & dysfunction. We're talking about serious decrease in both fertility and testosterone production, and at times testicular shrinkage. So while this might seem like a light topic, it is actually very important.

Boxers, & Trucks: Do a slightly better job at cooling the testicles, but, they still trap a lot of heat and provide no scrotal support. This means both overheating and scrotal sagging. We can do better.

Going Commando: Going commando is a great way of keeping the testicles cool. And... It works! But, unfortunately, it does not provide testicular support, leading to scrotal sagging. So, it is better than boxers and trucks.

The Best Underwear For Cooling The Testicles: This type of underwear maximizes cooling while providing testicular support & penis/testicle separation.