Boxers provide no benefit for varicocele because they trap heat, and do not provide no support. This means both scrotal sagging (increased varicocele size) and overheating. 

Do not wear briefs if you have a varicocele. The main problem with briefs is that they squish the testicles and penis together into a ball. This traps lots of heat. Compression and with over-heating creates testicular dysfunction (it prevents the testicles from dropping to cool, and over-heats them too.)

Scrotal support underwear has the exact same problem as briefs. They compress the testicles and penis into a lump, over heating them and preventing the testicles from dropping to cool. They cause a lot of damage to the testicles. Many ill-advised doctors recommend scrotal supporters for those suffering from varicocele. 

I advise going commando over wearing boxers, briefs, or supporters. Cooling should take precedence over compression. Without cooling compression is dysfunctional. 

The best underwear for varicocele provides maximum cooling, separates the penis and testicles, and provides healthy scrotal support & compression. These combined together are very beneficial for varicocele. They help cure varicocele pain, reduce swelling, and improve both fertility & testosterone. 

When you combine compression, overheating, and varicocele, you get testicular damage. If you copress the testicles you prevent them from dropping down to cool-down when they're over-heated. From here, we know that varicocele disrupts normal testicular cooling. So, the testicles are almost always wanting to drop down to cool. But if you compress them up, they cannot even do this. Add poor heat ventilation to this, and you not only trap lots of heat, but your testicles have no way of cooling down. This means testicular damage--as in testicular shrinkage, infertility, and impaired testosterone.

Think of it this way: When the testicles are too hot, the cremaster muscle loosens and distances the testicles from the body in an attempt to cool the testicles. So, if you take away this ability with compression, and also add heat stress--that's a really bad idea. ​

Now, here that's actually that most doctors are getting wrong. Doctors are recommending supportive underwear for testicular pain, varicoceles, infertility, etc. They're treating the testicles like a joint "provide compression to improve blood circulation". But, the testicles aren't a joint! While some light compression is likely beneficial, too much compression is not. Moreover, compression with over-heating leads to terrible stress & damage to the testicles.

​Proper Testicle Support: Underwear that provides testicular support or compression Must also provide adequate cooling. ​