neoprene covers help keep the smell outa my truck. it doesnt let the farts sink in and sit in the seat...in my dads truck(chevy trailblazer) he has to carry a bottle of freebreeze in there. you bust ass and it lingers for a few days. and you dont smell it until you get up and leave it sit for a while. open the door and its like a gas chamber. he leaves the windows down every night now in the garage to get the "ass" outa the truck. so if anything, the neoprene prevents seepage of ass....plus they're water proof. mine are stained from where stuff has spilled...just throw em in the washed and they're good as new.

PS. i have the xterra covers.