I just ordered some 303 Protectant for the vinyl top on my Miata.
The product suggests that I first wash the top with "soap" and not "detergent"
There's a difference?

They mean don't use something like dishwashing detergent (except in rare cases you shouldn't use it on the car anyway)- they're harsh on vinyls/fabrics, and strip wax.

Use a non-detergent based auto wash, or other products designed to be used on your car.

If you have dirt build-up in the "grain" on the vinyl mix up some car wash in a spray bottle, soak the area, and rub lightly with a "magic eraser" - works like a charm (on interiors too).

Nial,
Soaps are the salt of animal fat (tallow) and / or vegetable (i.e. coconut) oils / fatty acids. Soap would be considered a natural surfactant. Detergents are the synthetic version of soap and are often petroleum derived. Technically soap is a detergent but this is the difference they were talking about.

You can often read the ingredients or find the MSDS and tell if it is synthetic or not. A popular liquid car wash concentrate lists Sodium Alkyl Aryl Sulfonate and Sodium Olefin Sulfonate as ingredients which would make it a detergent / synthetic. If the ingredients have "petroleum distillate" or "naphtha" then it would be synthetic as well. Also assume that if it is a granule it is synthetic.

Sorry, I cant be of much more help regarding soap vs. detergent, but if you have not used 303 before, you'll like it. works great on just about everything, I use it most on my kevlar canoe to prevent fading.

Steve

Going back and reading my 303 brochures, I'm surprised they even mentioned using soap and not just their cleaners.

Here's a tutorial on cleaning tops by the way: http://autopia.org/forum/guide-detailing/80227-convertible-top-care.html

Aerog's post is spot on and is also supported by the reference he provided. "Car Wash" is for cars, Detergent is for the laundry and dishes.---Fwiw--Keoke

Wow!
Thanks to all for the great info!

Good resource, thanks for the link.