Sound deadening is made of a butyl rubber material which lowers the frequency of vibrations and thus make them quieter. Vibrating metal from the movement of the van is largest source of noise while driving. This is applied to the walls of your van before you insert the insulation. 

This product is sold in 40 sq. ft batches

Example vehicles: 

SPRINTER 144 WB // 80 SQ. FEET 

FORD TRANSIT 148 WB // 80 SQ. FEET 

PRO MASTER 159 WB // 80 SQ. FEET 

SPRINTER 170 WB // 100 SQ. FEET

SPRINTER 170 WB EXTENDED // 100 SQ. FEET