Thanks for the kind comment!
Armor is a flat damage reduction with some adjustments when the armor is greater or equal to the damage (with 20% chance, the blow is avoided and with 80% chance, the attack inflicts 1 HP). I agree that the game is difficult to read though. I wanted a minimalist UI (due to the limited screen size) but it makes the game more difficult to grasp.
You can hover a blob to know its HP :) It's now written on the game's page thanks to your comment.