Blast Protection is a gear perk that improves your defense against explosions. Grenades, rockets and tank shells all hurt you less.
Explosive damage to you is reduced. That matters most in fights with tanks, launcher troops and helicopters.
Wear one of the gear pieces that carry it: Impact Helmet, Impact Slacks, Impact Vest. Each piece only takes one body slot, so plan around the other perks you want.
Good if explosions keep killing you. Blast Defender is stronger if you can fit it in the same slot.