Originally Posted By: sleddriver
1. If they're that bad, you may decide to toss them & buy new.
2. Otherwise, add enough really HOT water to a bathtub to cover the mats an inch or so.
3. Use Tide or Whisk laundry detergent. These regularly win the CR laundry detergent tests. Add enough to the water to make the solution
really slippery. Aggitate it well to fully dissolve.
4. Add the mats UPSIDE DOWN as they'll likely float and you need the carpet surface to remain saturated at all times.
5. Add plastic or bubble wrap on top to retain the heat for as long as possible.
6. Let it soak for ~ 24hrs.
7. Turn over, scrub both until your shoulders hurt.
8. Evaluate & repeat if necessary.
Sounds like you got that car mat cleaning down to a science.