Splint Mail is a type of medieval armor and a very common item of equipment in most Fantasy Role-Playing games. This type of armor never gained widespread popularity because of its inherent drawbacks.
Every suit of splint mail begins with a standard suit of either chain mail or leather armor. Metal strips are then riveted vertically up and down the torso area. This is not the most intelligent design. The human body tends to flex from back to front quite a bit in combat, and this armor design severely restricts that movement.
Splint mail can also become dangerous to the wearer, as broken splints tend to jab the wearer. This combined with the extra fatigue brought about by more difficult movements, makes splint mail a rather undesireable form of protection.
Just as ring mail gave way to chain mail, splint mail eventually gave way to banded mail, which is a far superior design based on the same idea. Some armorers continued to produce splint mail long after the advent of banded mail, simply because it is not a difficult form of armor to produce.