As mentioned by others, there are a couple of concerns when treating the top.
The principal failure mode is exposure to sunlight which breaks down the fabric at the molecular level. UV protection is the first thing you should be looking for if you love your top.
Second is the rest of the environment. The canvas material is actually made up of several layers. One of the layers is nearly impervious to water. It is what keeps the water out of the car. Beading is an interesting and some would say attractive side effect of treating the top but the real reason you treat the top after UV and why you like beading is because another failure mode for the canvas is friction. If your canvas is exposed to a lot of fine dirt or worse rock dust, and that dirt / dust gets carried into the weave of the fabric, then it can act to mechanically damage the structural integrity of the canvas weave. The more you keep dust and dirt out of the weave, the less chance for mechanical wear.
This has been hashed out in the past
Here is what I was told by the guy who owns the company and made the canvas for out tops. We shared a telecom as well but I am not at liberty to share that with you.
"I got this response from Haartz
Thanks for contacting The Haartz Corporation.
In reply to your inquiry about the RaggTopp Cleaner and Protectant system, Haartz continuously studies the market and internally evaluates various products for performance. The below bullet points are a overview.
• Comparison testing according to proprietary internal Haartz soiling/cleaning methodology has shown Raggtopp to be among the best cleaners on the market.
• RaggTopp protectant has been shown to offer comparable spray rating performance when tested according to AATCC Test Method #22.
o The above has been achieved without the use of silicone in the protectant.
• The formulations of the RaggTopp cleaner and protectant have been shown to have no negative effects upon the long-term durability of the topcover. Both avoid the use of organic solvents that can damage the fabrics and combining layers between.
• RaggTopp cleaner & protectant have also been shown to have no negative effect upon materials adjacent to the convertible top (plastic/glass window, paint, etc.)
I hope that you find this information of value.
THE HAARTZ CORPORATION
If you want to read the entire thread from 2007 here it is.
Draw your own conclusion. I have not dog in this race, but am interested that when people make a decision it is an informed decision.
RaggTopp vs. 303 - Pontiac Solstice Forum