Antivibration noise dampening shims are designed and manufacturered to fit SPECFIC OEM Brake PADS. They usually help non oem pads but not as much as oem.
Ever wonder why most after market pad companies don't spend the $250,000 to test and design shims for their pads on every car the composition is used [offered for sale].
The slot length and width and curved shape are the tuning along with multilayer thickness of dampening material.
This explains how some parts of the shims work to reduce noise:
http://www.scielo.br/pdf/jbsmse/v26n3/a ... f90318.htm
Understanding BRAKE SCIENCE will be useful all your driving life!
EaglePicher Wolverine makes over half the shims used in US and 86% of Asian vehicles:
http://www.wolverine.cn/files/pdf/shim.pdf
.005"ACTIVE MATERIAL(Nitrile Rubber) on both outer surface is critical! Why shims should be replaced every other pad change!