Rose Buckler

The Rose Buckler is an Uncommon item introduced in Risk of Rain 2. It grants the player 30 armor when they are sprinting. When this effect is active a ring of round shields floats around the character.

"Armor" means any damage taken is multiplied by 100 /(100 + armor). This means one active Buckler reduces damage by a little over 23%.

Trivia
The in-game info claims the armor value to be 25%, but the real value is 30%.