Bread feels soft because it contains water. When bread is left on a table, some of that water slowly moves into the air.

This process is called drying. The outside of the bread loses water first, so it becomes hard before the center does.

Air temperature also matters. Warm air can hold more water, so bread may dry faster in a warm room. Moving air, such as wind from a fan, can make the process even faster.

A plastic bag slows drying because it keeps water near the bread. However, too much moisture can make bread sticky or moldy.

The best plan is simple. Keep bread covered, use it soon, and freeze extra slices if you need to store them for a longer time.