I want something very temporary for my Mitsubishi for my long highway trips, but I'm worried that I'll raise the internal temperature too much. Would a mattress foam work? The squishy kind that you put under your bed sheets. I think that it could alleviate potential overheating, while at the same time providing some drag relief. The material is covered with tiny perforations which at a high speed could allow small amounts of air in. I assume you could poke more of them into it if need be.
What do you guys think? I have yet to do any aero mods to my car yet, mostly because the body, paint, and the rest of the car look great!
I don't think the foam is worth the effort. It's not going to provide adequate airflow at any speed if airflow is in fact an issue for you, but consider this:
The cooling system of the modern car is designed for the worst conditions you can throw at it, i.e., towing with a full car on a Las Vegas hot kind of day. Cars may not maintain that kind of efficiency as they get older, but they are certainly capable of it initially. Just watch your temp guage.
as other said alum, I had some alum flashing laying around the garage so I used the cut it to fit the whole in the bumper and then used some zipties to attach it, lightweight and cheap did the trick a coat of paint and you'd never notice it...