Dynamat has kits available with enough to do an average floor. I like the Extreme kind with it's extra thermal layer. You don't need to cover every last square inch, but make sure all floor panels, doors, trunk panel, ect. have at least 80% covered.
I just finished using dynamat on pretty much every square of my interior (floors, doors roof). I still have the floor under rear seat to do (just need to buy the material). In terms of sound reduction, and less heat from floor, it made a huge difference. To cover entire floor, you would need at least one bulk pack. I bought one at a local car stereo place for about $200. For the entire interior, I went through roughly 3 bulk packs, maybe a bit more. One sheet of the 'dynomat extreme' will reach from edge of sill plate middle of floor pans (where transmission tunnel hump is takes a little more material). You probably dont need to cover every square inch, that is just what i chose to do, and the results were great (and worth the price). I would at least cover 80% of the metal like Bill mentioned. I'm going to try to attach a picture of what the front portion looks like for my floor. (Even under the pedals, where it is just black, that is another type of sound deadener somebody gave me, so I used it too.) Good Luck.
I believe that dynamat is mostly for sound deadening. If you are looking for thermal (heat) insulation, you can buy a thin (approx 3/16)sheet product (don't recall what it is called) at Home Depot or similar stores. It has one side that is shiny foil and is used as a thermal insulator. It is considerably cheaper than dynamat. Dynamat is very dense and prevents body panels from resonating and transmitting sound. I don't know how good it is as a thermal insulator.
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