I had the seat out While installing my new top anyway so I figured it would be a good time to do some work on the "Miata hot foot" problem that my car has always had. I lived with it for years but now was time to do something about it. I purchased a 4' x 25' roll of Reflectix from Home Depot for $42 + shipping:

A close up of the label in case you want to order directly from them:

Start by removing the seat (four 14 MM bolts at the edges of the seat rails). These things are notorious for being hard to get out. Mine were no different and I pretty much destroyed two of them during the removal. Roll out a 48" x 28" section and cut it off:

Put the reflectix on the floorboard and do a test fit. I didn't do a good job of taking pictures of this but you are putting the reflectix under the carpet as close the center console as you can. Since the console was out it was fairly easy to move the reflectix around under the carpet. Trim what you need to:

No need to glue it down. Just let it sit under the carpet. After a week of driving like this I noticed that the tranny tunnel was still pretty warm under the center console. I did some measuring and cut out a 20" x 7" section to go under the console:

There are a lot of holes and sections you need to cut out of your console shield but it doesn't take too long.: