Traditional bar soap is happiest when it can dry between uses. Good storage helps keep the bar firm and reduces unnecessary softening.
Use a draining soap dish
The simplest option is a dish or rack that lets water run away from the bar. Avoid leaving the soap sitting in a pool of water.
Let the bar dry
After washing, place the bar somewhere with airflow. If more than one person uses the soap, make sure it is not constantly wet between uses.
Don't store it in a sealed wet container
A closed container can trap moisture. If you use a travel case, allow the soap to dry before closing it where practical.
Can you cut the bar?
A large bar can be divided into smaller pieces for easier handling. Keep unused pieces dry and clean.
How long will it last?
There is no single lifespan because use frequency, water exposure, storage and the amount used each wash all affect how quickly a bar is consumed.