Light Plating is a technology that can be researched at the War Center in Tech Level 2. It costs 100 Food, and gives Mech Factory units +1 armor and +1 pierce armor. It must be researched before Medium Plating becomes available.
Since the only Mech available in Tech Level 2 is the Scout, which is rarely used in combat, this technology is of limited usefulness early in the game. For most players, it makes more sense to wait until Tech Level 3 before researching it, when Strike Mechs and Mech Destroyers enter the battlefield.
"Much like basic armor for Troopers, this Tech Level 2 technology boosts the defensive ratings for Mechs."