What clears are best?
The answer is as cut and dried as they come, a Polyurethane clear.
All the normal production clears made by the majors are medium to low solids medium acrylic urethanes. Thinner and harder equals faster for production work and most are two coats and deliver with some recommending three coats to get proper mils.
One major spot repair clear you all know and has been out for years, used by many production shops, formula was changed a number of times and name a couple of times, now discontinued, reason? Cars would be repaired and if the guy drove on a gravel road or drove on expressway to work, the car would come back looking like it had been sandblasted in 6-12 months, clear had no flex but it was fast and easy to use for those insurance repairs.
Acrylic and polyurethanes are points people like to argue about if there is a difference but there is a big difference as far as the amount of coats you can apply without losing the durability of the clear, more chemical resistance and almost always higher solids.
Higher solids mean more ISO’s to kick to compensate for the extra polyol and get the proper OH/NCO ratio and the ISO’s them selves add more durability and chemical resistance to the clear.
If this is wrong, then why does every skydrol approved clear for aviation , has the name Polyurethane on it?
Why is the most expensive and best clears from the majors, Polyurethane?7800 Glamour clear until replaced with 7900 that failed.
2002 PPG mainstay for years.
These clears have the flexibility and the softness to give you the best stone chip protection IF you have prepped the car the right way as discussed earlier.
Also I did forget in previous post to list activating the base as one of the best things you can do, to help prevent chipping.
Hopes this helps as a book could be written but I tried to just make key points, so you know, chips have more to do with how everything is done, not just what clear you used.