How did a padded undergarment make chain mail safer to wear?

A padded undergarment was essential for wearers of chain mail because it provided a necessary buffer to protect the body against bruises.1

While chain mail is highly effective at resisting slashing strokes due to its flexible, interwoven iron or steel rings, it lacks the rigid structure of plate armour. Consequently, the force of a blow—even if the mail prevents the weapon from cutting the skin—can be transferred directly to the wearer's body. The padded undergarment acted as a shock-absorbing layer, mitigating the impact of strikes and preventing the bruising that would otherwise occur from the mail being pressed against the wearer during combat.12