For those of you with undercoating...

[Morpheus]

Is there any particular chemical that is best for removing it? Naptha, Paint Thinner, Acetone, Goof Off, or all of the above?

[David T]

Using chemicals or solvents is a very messy and dangerous way to remove the undercoating. Mechanical methods are best. The undercoating should be hard and brittle so a scraper, chisel, putty-knife and such should work well for the most part. Eastwood sells a spray can of solvent that works well after the bulk of the undercoating has been removed. 3M also has cleaners that will work well but again, they just make things messier. Snap-On sells a tool that makes quick work of removing undercoating but it isn't cheap and and is pneumatic so you need an air compressor. Don't use it where the undercoating is on fiberglass, only steel. It will destroy fiberglass. Use safety glasses and have plenty of ventilation. Keep a fire extinguisher handy and an eye wash station.
David Teitelbaum

[Morpheus]

The undercoating that is on my car is very sticky and rubbery, and thus is not very brittle. Hence, I figured that all it needs is the proper chemical motivation to be removed.

[Bitsyncmaster]

The undercoating that is on my car is very sticky and rubbery, and thus is not very brittle. Hence, I figured that all it needs is the proper chemical motivation to be removed.

Mine is undercoated and is soft like yours. Any solvent will take if off but like everybody has said.....big mess. MEK is my choice for removing anything but needs to done carefully. I'm leaving mine undercoated since I don't want to tackle the removal job.