[NitrousG35]

Hoodliners are used primarily for soundproofing. As I said earlier, more expensive cars have them and they can be quite thick at times. They also can serve as a fire retardant [not so important on a fuel injected motor, but definitely important with a carburetor]. Lastly, they can provide a degree of thermal insulation, which can benefit the paint on the hood. I am not sure how effective they are at keeping an engine warm in the winter. Here in Minnesota with sub zero temps, you need more than a hoodliner to keep an engine warm. As for keeping an engine cool, I think it has just the opposite effect. Back in the day, guys used to remove it because underhood temps were higher, which was bad for the intake. More hot air ingested=less power.