I stumbled across this thread and thought I might be able to clear up a few things:
1. The key measure of how much heat is absorbed from sunlight is the Solar Reflective Index (SRI)
, which is directly proportional to the reflectivity & emissivity of the entire spectrum in sunlight (not just infrared), i.e.: high reflectivity & high emissivity = higher SRI.
2. The single most important value is the long-term (3-year) SRI,
which is intended to measure the degradation due to weathering & dirt accumulation.
3. The best way to determine which paints or roof coatings is to check the Cool Roof Rating Council product directory:
coolroofs.org/directory (column headings allow sorting on 3-Yr SRI).
If a US-based seller/manufacturer of roof membranes or coatings is not listed there, it is very likely that they are not entirely 'on the level' (maybe not an outright fraud, but could be re-branding & reselling coatings that end-users could buy for a lot less).
4. Paints that appear to the same color or lightness do not necessarily have similar solar reflectance. For example, with most paints, a flat finish typically has a higher SRI than a gloss finish (because gloss finishes usually have lower emissivity), but there are other non-obvious aspects that also affect SRI. Some coatings are designed to allow darker colors to reflect more solar energy than a similar color 'ordinary' paint. Check this chart:
and the photos on 23 & 24 of this publication:
That said, while there are several other factors besides the apparent color that significantly affect the SRI, the paints/coatings/membranes with the highest SRIs always appear very bright white to the human eye.
5. Most 'cool roof coatings' (like the Henry Solarflex mentioned in this thread) are relatively thick "liquid-applied elastomeric membranes" with a final thickness of 25 mils or more, which also means relatively low coverage (~ 50 Sq.Ft/gal). But there are also coatings with a typical final thickness of ~4-5 mils designed for use on sheet metal roofs or siding that apply much more like ordinary paint, with correspondingly higher coverage (150-200 Sq.Ft/gal).
Most this type (along with pre-finished metal roofing panels) that have the highest SRIs use Arkema's Kynar PVDF resins and a lot of titanium dioxide pigment, both which are uniquely well-suited to this task, and which have been used in high-end manufactured metal roofing for decades. AFAIK, none of the manufacturers of the highest SRI 'paint' products in CRRC make any claims about using "ceramic beads" as the "secret" behind their effectiveness. Examples of 'paints' with some of the highest long-term SRIs available: Tex-Coat Reflect-Tec, Nutech NXT Cool Coat, and GAF Kymax Coating. Though some of these aren't cheap, their much higher coverage makes them as affordable as mid-range acrylic roof coatings sold at Home Depot.
A few mainstream, readily available, competitively-priced roof coatings/paints do have "ceramic bead" additives, e.g.:
...but their SRI ratings prove they do not have higher solar reflectance than other similar coatings without "ceramic bead" additives.
6. The idea being promoted by some marketers that "ceramic beads" in paint are exceptional is misleading because almost all paint or roof coatings have fillers that, strictly speaking, are ceramic beads. Even the pigments used would also be considered ceramics. Commonly available user-added anti-slip additives are another example of this type of filler.
The commercial/industrial sectors in the US has developed just about every highly effective product imaginable for almost any application, and this competitive marketplace drives innovation. While it is true that coatings with the best performance cost more than more economical coatings, the likelihood that a break-through product is available to end-users from an online vendor but not widely available & or widely used in larger-scale commercial applications, is extremely low.
I think most people would be a lot better off buying mainstream products from reputable retail outlets. Maybe you'll have to special-order it, but if you can't get it from Lowes/Home Depot or one of your local contractor supply wholesalers, odds are it's not going to be a good value for your application.