For optimum sealing performance, correct o-ring selection is the direct result of a number of design considerations. These considerations include: size, squeeze, stretch, chemical compatibility and the ability to resist pressure, temperature and friction. All of these points of o-ring design are covered in detail within the sections of this Seal Design Guide. Often, there are a number of materials that are appropriate for a particular application. Consideration should be given to the full range of environmental and cost factors. Your final selection will usually be a compromise in the sense that you have to balance all of these considerations.