Heat. OMG the heat
 

I don't remember the exhaust putting off so much heat. Everything on the passenger 1/2 the car is very hot..

Yep. On my race car the bottom side of the right side of the car is covered with DEI Reflect-A-Cool sheet. They sell it at the Autozones around here in 12x24" sheets. It has an adhesive back and will stay put as long as the surface you are attaching to is clean. In a pinch, I have used pop rivets and fender washers in a few places to hold it in place. I use foil tape around the edges to seal out oil. Has been on the car for quite awhile and it makes a difference.

What ever you do, don't wrap the exhaust, insulate the floor instead.

Most effective way would be to keep the heat in the exhaust pipe itself: White Lightning Exhaust Coatings | Swain Tech Coatings | Industrial Coatings | High Performance Racing Coatings The factory exhaust systems have heat shields everywhere for a reason. We need to mimic this when installing aftermarket exhausts systems. DEI, mentioned above, also helps thus a combination of a few techniques may be needed for the best results.

The exhaust tends to die when you wrap it. I'll check out what AutoZone has for reflective barrier . I'm not sure if coatings have the same affect however their quite expensive comparatively. I also made the mistake of having my hood cracked open near the cowl. That hot air gets sucked I to the cowl and into the car through the outide air ducts . Good times!