Abstract: A pair of like adjustable masking mats for variously sized rectangular storm shutters, each including top and bottom L-shaped panels. A longitudinally oriented elongate groove is disposed on the back side of the long leg of the top panel while a complementary inwardly expanding elongate tongue is longitudinally disposed on the front side of the long leg of the bottom panel. The tongue interlocks and longitudinally slides within the groove for slidably interlocking the top and bottom panels together in a longitudinally contractable and expandable U-shape arrangement. Hand operable locking hardware is provided to releaseably hold the top and bottom panel stationary with respect to each other once the panels are sized for a particular shutter.