they are a think plastic which protect the wheel wells really well! and they clean up really nice and easy. when I wash my truck and shine my tires I just spray some tire shine in there too and it looks great! they are pretty much the same at the front wheelhouse liners but for some reason they don't put them in the rears. The avalanches have them but not the silverado's for some reason.... I tell everyone that gets a truck they're a must!
Congrats on the new truck and welcome to the club, a definate first and a must have are wheel house liners! If you look at my albums there is a pic of what they look like and here is the link to the site where I got mine.