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There are many Polymers that may be used depending on the specific application
Natural rubber or tree rubber was the first form of rubber to be used in the manufacture of inflations, it has great dynamics for quick response to opening and excellent cut resistance however it is very susceptible to oil swell and attack to oxidation even when compounded with extra protection. These parts may be used for 600 to 900 individual cow milking's (ICM) Synthetic Polyisoprene is a polymer that has been man made with the major chemical structure similar to Natural Rubber. Developed in the mid 1950's this material can be used in place of Natural Rubber where certain proteins may cause skin sensitivity. Synthetic Polyisoprene does not have the tear or cut resistance of Natural Rubber but is processed easier with Banbury and Mill mixing. Styrene Butadiene rubber by itself lacks both the dynamic and chemical resistant properties to be used alone and most often is used as a extender or in some cases a chemical link to help bond several less compatible polymers such as Nitrile and Natural. Nitrile rubber is one of the best materials for resistance to oil swell however it lacks in dynamics and the cut resistance of some other polymers. Virgin Nitrile polymers lack strength and are compounded using high amounts of carbon blacks or silica's, to achieve a soft feel the Nitrile rubber must be heavily loaded with oils which will cause the part to become even less dynamic. Nitrile compounds quite often incorporate SBR or the combination of SBR and Natural rubber to get a proper mix of desirable properties. These parts may be used for 900 to 2500 ICM depending on the ratios of Natural, Nitrile and SBR. Silicone rubber has been used to a limited extent in manufacturing inflations over the past 15 years. There are several draw backs to silicone, the product has very poor tear qualities and can easily be punctured. Although it has great ozone protection and oil swell properties it does however allow oils to permeate through the walls of the part which for transparent parts makes them totally unacceptable. With proper care and design 3000 to 8000 ICM's have been achieved. Urethane rubber has been recently approved for use in inflations it has been very successful in the medical and packaging fields, due to it's very low oil swell, the high tensile strength (toughness) and it's properties of cut resistance. Compression set and a hard durometer (55 Shore A) appear to be 2 marks against the material! It could go as high as 10,000 ICM's before replacement is required. Thermoplastic rubber may be where the future of inflations is headed in the 21st century. There are currently many materials in this category that lend themselves to the manufacturing of inflations. At this point there are few thermoplastic rubbers that will meet the FDA guidelines for repeated contact use however most suppliers of the materials do not realize the size of the markets annual requirements (as high as 100 million lbs.). Thermoplastic rubber can be compounded with all of the good attributes of Nitrile, Natural, SBR and Silicone rubber but with more consistency, cure cycles are in seconds not minutes. ICM's could be comparable to those of Silicone. EPDM rubber has not been the choice of most inflation manufactures even though the dynamics of the polymer gives it good flexing and rebound. The ability of the rubber to remain stressed (elongated) for months without loosing it's tension makes it a good choice for tarp straps. Windshield wiper blades and the use in rubber roof membranes are common uses for EPDM because of the inertness to ozone degradation. Two of the reasons for some manufactures not using this material are the susceptibility to attack by both chemicals and oils which are prevalent in the contact with inflation use.
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