Which flooring? Tiles, vinyl, or parquet? Tips?

Friends tiled the whole house because with underfloor heating it is supposed to be nice and warm - so they thought, but the underfloor heating is never on in summer and then tiles just always feel cold. They have noticed that now.

Sorry, but that’s nonsense.
Tiles do not feel cold in summer at normal room temperatures above 20°.
If they did, I wonder why 99% of all bathrooms are tiled. Especially there people often walk barefoot.
Not even my wife finds the tiles too cold, neither in summer nor in winter. And that says something.

But maybe it also depends a bit on the tile and/or the insulation underneath?

Could be due to the insulation. Upstairs I don't notice any difference between parquet and tile, downstairs there is a slight difference. Neither my daughter nor I am bothered by it. Even my husband has not complained yet.

Sorry, but that's nonsense. Tiles don't feel cold in summer at normal room temperatures above 20°. If they do, I wonder why 99% of all bathrooms are tiled. Especially there, people are often barefoot. Not even my wife finds the tiles too cold, neither in summer nor in winter. And that says something. But maybe it also depends a bit on the tile and/or the insulation underneath?

Why should that be nonsense? Stone always feels colder than wood unless it is heated. But in summer it never is (except in the bathroom). So it feels cool at first. But it's certainly a matter of personal preference. Just a point worth at least briefly thinking about; if it doesn't affect you, that's fine too.

Why should that be nonsense. Stone always feels colder than wood, unless it is heated. But in summer it never is (except in the bathroom). So it initially feels cool. But it’s certainly a matter of taste. Just a point to at least briefly consider, and if it doesn’t affect you, that’s fine.

I also have different floor coverings and therefore the topic concerns me as well. Why should the floor in the bathroom be heated in summer? It doesn’t need to be; it is warm enough without additional heating so you don’t get cold feet. In summer, the heating is off.

I am bothered by generalizations like “tiles are always cold.”

We do not have underfloor heating and yet there is no difference upstairs and only minimal difference on the ground floor.

In general, tiles "feel" colder than parquet, for example. But: In winter, the tiles are warm with underfloor heating. When the sun shines in, the tiles are also very warm in summer (wherever the sun hits). And in summer, I also see no reason to heat tiles in the bathroom (in my opinion, that's nonsense). I always want to have tiles in the bathroom: warm in winter, cool in summer (when it’s hot outside). In the living areas, we will certainly have parquet in the next house build (kitchen is still unclear). Everyone feels floor coverings differently: Therefore, you probably cannot establish any "generally valid rules".