The waterproof protection you get from a convertible top comes from the butyl rubber core sandwiched between the outer canvas and the inner pre-shrunk cotton layer. An applied protection only renders the fabric water resistant.
Rode & Schwalenbert Gmbn. (Germany) the world leading manufacturer of automobile convertible tops exclusively recommends Harrtz RaggTop Cleaners and Protectant. Developed specifically for cleaning, re-proofing and preserving convertible tops, these cleaning kits consist of two products:
1.Cleaner to remove soiling, stains and atmospheric pollution for both natural and synthetic materials. The best cleaners are formulated from low-pH (low alkalinity) and gentle enough for repeated use over years. They will rely on proteins and enzymes for their safe, but effective, cleaning power.
2.Fabric protector to re-proof and preserve fabric tops from the effects of water absorption, surface soiling and staining, and provide a sunscreen from UV radiation and subsequent fading. It has the best UV protection of any product on the market, and it repels dirt, grease, and oil. It doesn’t make your vinyl top glossy or greasy-looking. It will have the natural matte sheen of new vinyl.
this is the fabric protector recommended by Glen Raven Mills (Sunbrella) and the Haartz Corporation, 303™ High Tech Fabric Guard restores lost water repellence and stain repellence to factory new levels. It stops leaks, resists soiling and impedes mildew formation and helps protect against the sun's harmful UV rays.
For more information see article “Convertible Top Detailing ”
in the Detailing School
section of Detailing Bliss forum...