Plenum is the part located between the front windshield and the bonnet of an automobile . It is primarily used as an air inlet to the HVAC during fresh air mode operation. It’s secondary functions include water drainage, aesthetic cover to hide the gap between windshield to bonnet, concealing wiper motors and mechanisms etc. The plenum consists mainly two sub parts viz. upper plenum and lower plenum.Conventional plenum design which is found in majority of global OEMs employ a plastic upper plenum and a metal lower plenum which spans across the entire width of engine compartment. This conventional lower plenum is bulky, consumes more packaging space and has more weight.In this paper, we propose a novel design for the plenum lower to overcome above mentioned limitations of the conventional design. This novel design employs a dry and wet box concept for its working and is made up of complete plastic material. This proposed design consumes only about 1/3rd of the packaging volume with a weight savings of up to 50% compared to a conventional plenum in similar class of vehicles. This novel design is of modular architecture. This enables the design to have a potential of standalone unit which can be cross deployed in similar class of vehicles instead of going for new development, thus allowing significant cost savings.An optimized and structured approach for testing of the plenum is derived to correlate testing conditions in the real world conditions. The proposed new plenum design is observed to perform better in all test parameters and was implemented on vehicle.