When you use Brace, you gain 2d10 Temporary HP instead of the amount the Ability would normally provide. All the same rules regarding the Temporary HP from Brace still apply. In addition, using Brace causes you to Deboost all Damage you take as long as you remain stationary.
Note: Any extra damage dice rolled due to a Boost or Critical Hit are added before the Deboost from Improved Brace takes them away.