Waxed paper or tinfoil prevents smoke from infiltrating the paper and almost completely stops air exchange, so going with an unwaxed paper allows you to get more flavor and slightly more exchange for optimum bark retention. You still want it fairly thick because you need to keep the humidity up inside -- humidity encourages your collagen (one of the main binders in the meat) to convert to gelatin, which is what takes your tough, connective-tissue-filled pieces of meat and turns them into moist, tender, delicious competition BBQ with a silky mouthfeel (from the gelatin).