We borrowed this pic from Aquadoula®, hope they don't mind.

Our comfy Aquadoula® tubs are designed specifically as labor pools. They are 4½ feet in diameter and 2 feet deep, and fit two adults with room to move.

The rigid walls are foam-lined for comfort, yet provide complete support for bracing during pushing. A built-in, thermostat-controlled heater provides maximum convenience at a time when you have more important things to do. A new liner covers the entire inner and outer surface of the pool for optimum hygiene. All fill hoses are drinking-water grade and non-toxic.