The GM felt liners are fantastic. They are flexible, durable, and tone down the noise level A LOT. I dont know if its becuase they are felt vs plastic, but they quieted down my road noise levels considerably.
I've had the felt ones on the front and rear for approximately 125,000 miles and they still look new with no rips, tears, or wear marks, and I DO off road my truck in muddy and rocky terrain. I was VERY hesitant about the felt liners at first, but I went ahead and purchased them with my free GM rewards points when I bought the truck, and I will never go back to the plastic ones if I can help it, these are just too quiet, easy to install, easy to clean with a pressure washer, and durable. The only two aftermarket accessories that GM provides that are a better value than the competition are the felt wheel liners, and their aftermarket rubber floor liners similar to WeatherTech, but infinitely more durable and flexible.. They nailed it with those two.