The Safety Reason Behind It
The most important reason for this trick is not about comfort. It is about safety.
In a fire emergency, smoke can spread quickly through hallways. If the hallway outside your room is unsafe and you cannot leave immediately, emergency advice often includes staying behind a closed door and sealing gaps where smoke may enter.
A towel placed at the bottom of the door can help reduce the open space beneath it. In an actual smoke emergency, a wet towel, wet sheet, or wet clothing may work better because moisture can help create a tighter barrier.
Of course, a towel is not a replacement for alarms, sprinklers, emergency exits, or calling for help. It is only a small backup measure. The closed door does most of the work, and the towel simply helps cover the gap underneath.
Still, it is the kind of simple detail that is easy to remember when traveling.
