Because foam has a larger capacity for filtration over cotton or paper

These kits allow you to tune your cars handling and reduce uneven tyre wear

Like All Hasport Mount Kits

or if you are having a custom CAI made

MERCEDES W117 BOOT LID SPOILER AMG-CLA45 2013 On - REPLICA - Celica (Mk7 (T230)) (1999-2006) Because foam has a largerMANUFACTURER : M2 Motorsport SPECIFICATION : Boot Lid Spoiler MATERIAL : Hard ABS Plastic MODEL YEAR : MERC W117 2013 Onwards Hard PU accurately moulded body panel that can easily except modern plastic primers for re finishing by professional auto body technicians. W117 2013 onwards rear boot spoiler in abs plastic.