Usually, when the tube is full, it become very firm. Covered tubes should be no wrinkle on the surface. An adult should be able to stand on the tube and only sink a couple of inches in the water.
Towable tubes need to be full of air and properly maintained for long product life and ultimate performance. In order to properly inflate and maintain tubes, you must have the proper equipment. Next time we will tell you how to choose Inflators. See ya.