In the case of WPC, people always refer to the fact that it heats up a lot. But doesn't that apply equally and even more to patio slabs / patio tiles / natural stone, etc.?
If something retains heat well, it already does not conduct heat well. Stone, wood, and plastic are poor conductors of heat. That's why they are used for insulation (there are better ones, of course). Metal, on the other hand, is a perfect conductor of heat. Plastic, on the other hand, is also not a good heat accumulator. Wood and stone are much better.
There is no general statement. It depends on the surface, but above all on the duration of exposure. Basically, I would always use materials with low thermal conductivity. Not only are they slower to absorb heat, but they are slower to release it. A metal plate heated to 60°C seems much hotter than a stone of the same temperature. However, if the sun is hitting the material all day, all materials get very hot.
I would consider WPC and stone on the same level. WPC heats up faster, but if it's so hot you can't walk on it, it's no fun on stone slabs either.
We have light gray wood fiberboard floorboards installed. They don't retain heat and get very hot in direct sunlight. Tiles and the like only retain heat longer, but even then you can't walk on them barefoot at 30 degrees and direct sunlight. So it doesn't matter at all that everything gets very hot.
It also depends a lot on the surface. A really smooth (perhaps darker) porcelain stoneware surface will be hotter than a rough concrete slab. Our granite window sills are hotter than sidewalk tiles in the driveway.
The smooth plastic surface gets very, very hot in the sun. Why don't you go to a large building materials store that also has WPC in the showroom and walk around barefoot?
WPC is made from a mixture of wood fiber and plastic, isn't it? Stone is a very good conductor and heat accumulator. Wood is not.
In that respect, comparable stone should always be warmer than this WPC. I don't think the numbers will help you because a lot is subjective.
I think it depends more on the color of the thing than the material. Example: brown teak gets very hot in the sun. Anthracite stone slabs too. Light wood, light stone much less. I assume the same thing happens with WPC.