You can thank me later.
Sweat Proof Shirts: Anti Sweat T Shirts & Undershirts | Thompson Tee
It's expensive if you're from the UK. Might be cheaper on Amazon.
I have real issues with sweating through t shirts in public. I can go through multiple layers and show pit stains.
These are life changers. To anyone who feels how I feel. Bite the bullet and order 5 or 6. 100% blocks sweat round the arm pits.