Disclosure: I get a small percentage of your purchase if you use that link to buy this clay bar kit.
I had 0 experience with clay bars. Never even held one in my hand, and when I went outside to my beloved V70 R to use it, I found I had no idea what I was doing. I had to go back inside and watch YouTube videos like this on on how to use clay bars.
Like everyone else who's used them, I'm now hooked and can't believe I went this long without it.The purpose of a clay bar is deceptively simple: to pick up dirt from the clearcoat, dirt that won't come off when you wash your Volvo. That's it.
If you've ever run your had across your hood after you've washed your car and felt tiny bumps, removing those is what the bar does. This kit comes with two clay bars and a spray that acts as a lubricant as you move the clay bar over the surface. When I was finished, the surface of my V70 R was like glass. Reflective, deep, buttery glass. I'm going to do my 850 in the next few days.
The kit also comes with a microfiber towel and -- as a nice touch -- a small bottle of Meguiar's Cleaner Wax, which is a nice compromise between single-purpose showroom wax and a general purpose cleaner. In other words, it's forgiving, made for us car owners who do our own wash/waxing.
After a wash, then clay bar, then wax, the surface of my V70 is so slippery and reflective a plastic bottle set on the hood will slide off. It's like a force-field that keeps stuff from sticking to the clearcoat. The shine is awesome.
Wow, very cool job. Don't be a stranger to the Detailing & Paint Care subforum 
.