From Brotato Wiki
Paddings gives +3 to your Max HP and a further increasing depending on your current carried materials. You gain +1 Max HP per 100 materials you have. This is updated dynamically, meaning that your Max HP will increase during a wave as your pick up more materials. But this Max HP is also lost when you spend your materials in the Shop
You can have up to 3 Paddings, giving you up to 3 Max HP per 100 Materials you hold.