Assuming that you haven’t forgotten to pay your gas bill, it’s because porcelain tile conducts heat better than that cozy bath mat does, even though they’re at the same temperature.
It’s a common experience that certain things feel colder than others. People talk about “cold steel” as if the blade of a sword were somehow colder than its surroundings.
Bakers like to roll out their pastry dough on a marble slab because “it’s colder.” Just touch a steel knife blade or a marble slab and you’ll have to agree: They do feel colder. But they’re not. The steel, the marble and the floor tiles aren’t one bit colder than anything else in the room. They just feel as if they are. If they have been in the same room for any reasonable amount of time, all objects will be at the same temperature as everything else in the room, because temperatures automatically even themselves out.
Hot coffee cools off and cold beer warms up. Let a cup of hot coffee and a glass of cold beer stand side by side on the table long enough and they’ll eventually come to the same temperature, the prevailing temperature of the room. (Nevertheless, you’ll still think of the coffee as “cold” and the beer as “warm,” won’t you?) The reason is that heat spontaneously flows from warmer to cooler. That’s because the molecules in a warm object are moving faster than the molecules in a cool object; that’s what temperature is: a measure of the molecules’ average speed. So when a warm object comes into contact with a cool one, its faster molecules will collide with the slower molecules and speed them up—that is, make them warmer.
If an object should happen to be initially colder than its surroundings, then heat will automatically flow into it until its temperature is the same as its surroundings.
Or if an object happens to be initially warmer than its surroundings, heat will flow out of it into the surroundings. We have found it useful to think of heat flow as if it were flowing water. Water always flows to a lower level, while heat always flows to a lower temperature. We might even say that temperature seeks its own level. It’s not just steel, marble and tile that will feel cool to your touch.
The temperature of your skin is a bit below 98.6 degrees Fahrenheit (37 degrees Celsius), while everything else in your room (except a hot radiator, perhaps) is at the room’s prevailing temperature—around 70 degrees Fahrenheit (21 degrees Celsius). So when you touch an object in the room, it will feel cool to your skin because it really is cooler than your skin. Heat will therefore flow from your skin into the object, and your heat-deprived skin gives you the sensation of coolness.