When i was working in Off Shore industry a customer came by with special demands. He wanted to order sliding doors that would resist a water column of 15 meters on both sides. A seal was invented to meet his recuirements. This seal able to follow door deformations due to waterpressure can be seen at the bottom of this pdf.
The seal is made out of a coextrusion of two types of unflammable rubber. The red hatched part of the seal is made out of a harder rubber. A harder rubber has a lower friction coefficient and will reduce friction between seal and framework of the door. When closing the (in this case) sliding door this hard rubber will be pressed down. To reduce this press down force (reducing it will lower opening and closing force of the door) a hollow tube is extruded in the rubber. When the hard rubber is pressed down the two arms of soft rubber will then automatically move upward. The end of these arms wil come in good contact with the framework taking care of watertightness. The thin arms made out of softer rubber cannot withstand the waterpressure. Due to its high thickness the central part of the seal can overcome waterpressure and reduce horizontal movements of the arms. The thin soft arms are unable to overcome this water force. Due to a high waterpressure the deformation of the door when pressed away from its framework will be high. The long arms can overcome this defomation without losing their functionality.
With this new seal also another disadvantage of the old seal can be overcome. A high opening force needed to open these sliding doors.