Elastomeric compression seals, gaskets, tubing, and bumpers are used throughout the world in almost every industry. Sealing products range from simple RTV caulking (applied by the user) to much more complex shapes and sizes for large doors or other pieces of machinery.
Arguably the most common seal design is the molded O-ring which can be configured to practically any size or shape and made from many different materials. O-rings mechanics have been studied for years and their performance under certain conditions has been well documented. In some instances, however, a simple O-ring (or sponge gasket) may not suffice. Say, the seal needs to be designed to mechanically lock in place on a door or the pressure required to effect a seal using an O-ring is just too high. That is when a custom extruded (or molded) part may be your best choice.
Compression seals, gaskets, tubing, etc. can be configured in practically any shape or size depending on the application. Compression seals can be simple round shapes or can include square corners with fabric reinforcement. Many different materials may be used depending on the application. It's ultimately important to ensure that the seal is specifically design for the application. Over engineering can result in cost overruns; under engineering may cause seal failure.