i would like to know,
how long is installation?
any warranty? What if during installation some parts is broken?
what if the interior is rattling / more noisy bcoz of the improper installation?
will the new car warranty void after installing this?
what is the different of 2 layer and 4 layer?
in the market only got this type of sound proof? is this the best?
after using few years time, will it cause any problem or it is long lasting?

u install on what car? got significant impact? only 4 doors? closing the door feeling more solid?