When taking damage, DR is applied before DT, meaning that an 80-point attack on a player with a DR of 30 and a DT of 20, the damage is first reduced by 30 percent, leaving 56 points. Due to the vast majority of Fallout 3's assets being brought over to New Vegas, the existence of DR was likely a mechanic that Obsidian didn’t have enough time to fully replace with their preferred DT. New Vegas is unique since both DR and DT are present as a combined statistic. Regardless of how much DT you’ve acquired by any combination of armor, perks or consumables, it caps at 85 percent.
On the other hand, Damage Resistance is a derived statistic from the SPECIAL System and reduces the amount of damage taken by a percentage rather than DTs outright subtraction.
