The reason the wax may be hard to rub off is due to the high carnuaba wax content in it. Pure 100% carnuaba wax is hard as a brick. In order to make it soft enough to apply to a car's paint, companies use chemicals and silicone to dilute it. Different companies put varying amounts of carnuaba wax in their waxes. Zymol waxes are at least 33% carnuaba wax, the rest being other natrual products, no chemicals. Unfortunately, you let this dry and it will take alot work to get it off. Carnuaba wax is the hardest natural wax there is hence providing the best protection. I can't vouch for how much carnuaba wax is in Griot's waxes. I too have used his "Best of Show" wax and it's pretty good, just don't let it sit for too long. Just a little FYI, if you want the most wax for your money, buy cans of wax versus the luid wax in bottles. They have put even more chemicals and silicones in it to make it flow, which means you are getting even less real wax for your money.

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1999 MB SL500 (110,000 mi)
2004 Volvo V70 2.5T (220,000 mi)
2014 Tesla Model S 85 (136,000 mi)
MBCA member