Liquid SiO2 paint sealants, such as Wolfgang SIO2 Paint Sealant and Meguiar's M27 Pro Hybrid Ceramic Sealant. When I first got into detailing, more than 10 years ago, the big debate at the time was around (paste) waxes vs (liquid) sealants. The then current generation of liquid sealants, such as Blackfire Wet Diamond (now Blackfire Paint Sealant), Wolfgang Deep Gloss Paint Sealant, and Menzerna Powerlock, were fantastically slick, and application and removal were incredibly easy; however, water behavior and durability were not on the same level as paste waxes such as 476, Dodo Supernatural Hybrid, or Bilt Hamber Finis. Since I've always been a sucker for great water beading, I gravitated more towards paste waxes, even building myself a small collection of various products.
I kind of fell out of detailing around six, seven years ago - just around the time that coatings were gaining popularity - and missed out on quite a few products (and brands!) being introduced and gaining popularity. When I got back into it about a year or so ago, I was researching what new products had come out, to determine which to purchase now that I was again in a position to put a little more effort into keeping the cars in good condition. While I did consider coating them, the lack of running water and power where they are parked at our condominium made the prep and polishing required before coating impossible; and while I also considered the various spray sealants that have come out in the past few years (indeed, the cars were basically maintained with Optimum Car Wax and Meguiar's Ultimate Quik Wax during the fallow period that I didn't have the time to devote to them), there is sometime about the tactile application and removal of a paste or liquid product that a spray wax just cannot match.
After a bit of a deep dive into the forums, Facebook groups, and detailing sub-reddits - reading dozens of threads and posts from the years I had been away - I realized that, overshadowed by the general focus and interest on ceramic and graphene coatings and sprays, the old liquid sealants had also received quite a bit of an upgrade in the years since, with formula updates and infusion of SiO2 addressing the main issues - water behavior and longevity - that I had previously had with them. I have since bought and used Meg's M27 and Wolfgang SiO2 PS; while obviously not close to matching ceramic coatings in terms of durability, they are significantly better than their predecessors in this regard, and in terms of holding up to repeated washing. Their water behavior is also fantastic, approaching those of ceramic coatings and meeting or exceeding the best paste waxes I'd previously tried.
If these products had been out ten, eleven years ago, I likely would have never gotten into paste waxes; indeed, I get a bit baffled at all the recommendations I still see for Collinite 845 or Jescar Powerlock, when products such as these SiO2 liquid sealants are at least as easy to use, and offer better durability and water behavior, while not being nearly as picky on the prep and having a clean base as a coating or coating lite. I guess the timing of their introduction - way after coatings hit the mainstream - mean that far fewer people have used them than would have been the case before, and thus they mostly get overlooked, stuck in between coatings which offer significantly longer-lasting durability, and older products that, though less capable, have had far more people use them, and thus have significant advantages in reputation and word of mouth.