metal soaks heat more not less. Metal is cheeper to use than a molded plastic, this is why ,most after market ones use it. Think about it, IF they worked so well and ALL companies are doing what they can to market a car withthe highest MPG. Then it would seem a no brainer to use what ever they could to boost MPG and HP.?why go with VVT, or DFI? Just pop a Cai and bada bing done, cheep. Turbos are the new thing but, they do not save fuel unless you are at no boost. step on it and it drinks fuel like a dry camel drinks water. these small liter ecobosted motors claim MPG that most will never see unless you drive at the speed of smell.
fact is the numbers posted by the makers of these things are BS. They use a false peramiters on a Dyno to give false numbers, to a public that would pay 100$ to tie magnets to thefuel lines and think it gets 20% getter mpg.