Folks often ask us which respirator to use for spray painting and automotive body work. There are some good options out there but the type of filter and respirator mask will depend largely on the kind of work you do, and how often you are doing it. The only safe solution for urethane paint is pulling clean air from a remote spot and that requires an airline respirator system like the Allegro 9200-01 System. But let's talk about basics first.
For instance, if you are sanding Bondo, grinding or doing other body work that is likely to create particles in the air, a standard 3M 2097 filter will grab everything down to 3 microns (that's 99.9% of all airborne contaminants) and keep it out of your lungs. The 2097 also has a thin layer of charcoal to absorb low-level odors. For flying particles and some organic vapor, you don't need a big expensive system.
And you've got lots of different options as to what type of respirator you can attach those 3M filters to. There are inexpensive options such as the 3M 6000 Half Facepiece Respirator for under $12. Of course, if you are doing this type of work every day, or working on a project that will take a significant amount of time, especially the painting, you are going to want something more comfortable and with a better seal like the 3M 7500 series silicon mask.
The most basic complete cartridge filter set-up for (non-urethane) spray painting is going to be the 3M 6001 cartridge with the 5P71 pre-filters and 501 retainers. Made of soft silicone, the 7500 series of mask is non-allergenic and super comfortable to wear for a long day in the shop.
Again much of the paint used on car finishes will be urethane paint because of the smooth finish it provides. Almost all of the commercial car paint contains isocyanates which are particularly nasty. Isocyanates cannot be filtered by activated carbon filters so additional measures need to be taken for protection against this hazard.
One more quick note on filtering options - Positive Air Pressure Respirator (PAPR) systems such as the 3M GVP-PSK Paint Spray System are a step up from regular respirators. These are highly mobile and push air up to the mask with a small fan instead of the wearer having to pull the air through the respirator cartridges. It makes it easier to breathe, and there is no fear of having the fumes or particles sucked into the mask as you work. Like the 6001 Organic Vapors cartridges, this system will handle most solvent-based paints, but it isn't going to work with paints containing isocyanates, at least not in a measurable, long-term way.
The real solution is an airline respirator. Instead of filtering the ambient air, systems like the Allegro Full Face Mask Airline Respirator System pump air from a clean atmosphere through a hose to a full face mask. It's a little more work moving the hose around, but less weight on your hips compared to the PAPR systems, and of course, a much higher degree of safety because as long as the area the pump is set up in has clean air, the worker has clean air.
Lungs aren't the only things that need protection. Protective eye-wear should always be worn, or a full-face mask such as the Moldex 9000 Full Face Respirator. Full-face respirators are great (and predictably more expensive) because they keep the paint and fumes away from your eyes and face. You can also keep paint out of your ears and hair by wearing an inexpensive spray sock.
So there you have it, the long answer to the question of which respirator is best for automotive work and spray painting.