Many modern progressive coil springs use "dead coils" that are in contact with each other at normal ride height. When these coils load and unload they can make noise. Wrapping a spring insulator around the dead coils reduces unwanted noise.
The Whiteline coil spring insulator is a 1.5 meter (59") length of insulator material, enough for insulating a pair of coil springs.
Fits all coil springs with 10mm to 13mm diameter. Note: The product photo above shows a yellow insulator, but the product you get will be black in color.