Headlight lenses on my 2004 elantra are fogged up

You'll need the following. Painter's tape or Masking tape, 2000, 2500, 3000 grit sandpaper, bucket of water, headlight polish (PlastX, etc) and microfiber cloths

Mask off around the light so you don't have to worry about sanding your paint if your hand slips.

Soak the sand papers for at least 15 minutes. The more water the better Using the lowest grit, start sanding in ONE DIRECTION ONLY,(side to side). Keep the sandpaper wet and dip it in your bucket of water frequently. Now dry the headlight and it should look all hazy

Switch to the next finer grit, and repeat the step above, but this time go in the OPPOSITE DIRECTION (up and down). Keep using water
Dry it again, and it will look better than the first time.

Repeat the process again with your finest grit. Again, OPPOSITE DIRECTION with plenty of water. Dry it off. It should look relatively new at this point. Remove the tape as it will contain bits of grit from the sandpaper.

Generously apply the headlight polish in a circular motion to the headlight

Using your microfiber cloth, rub off .. repeat several times with FRESH rags until the polish is dry and gone.

Now the headlight will look like new

I'm a big fan of a visit to the junk yard in this situation. The elbow grease is minimal and I can usually get a better quality part than I started out with that might need less work to restore, if any, espescially on Hyundai's.

There are many ways to repair this problem. I have tried a few and have found that the 3M kit seems to work the best and easiest. This kit is what you need and it comes with everything needed for around $20. Most auto parts stores sell this kit. http://solutions.3m.com/wps/portal/3M/en_US/Car/Care/DIY_Projects/Maintenance/Restoring_a_Headlight/?WT.term=3M+headlight+kit&WT.campaign=158&WT.source=google&WT.medium=cpc&WT.content=526571&cshift_ck=1365242620cs526571&WT.srch=1

In an auto parts store you can buy a lit to remove the fog. It just requires a little stick-to-a-tiveness. I also recommend using a UV protectant wax on the lenses after you get the fog off.