Foam compositions and wet bums!
The natural rubber (NR) latex foam removed from the RD350 seat pan in theory shouldn’t have been there. Around 1973 the Japanese motorcycle industry moved away from what’s known as NR latex to synthetic foams. The NR material was actually only around 60% genuine rubber with the remainder made up of various organic zinc and potassium compounds that were environmentally big no-nos. The other downside is that NR based foams have an open cell type structure which, via capillary action, allow water to run all the way through acting like a sponge. This is why many older Japanese seat bases are rotted through. My original seat foam must have been one of the last NR types before the transition to polyurethane or PU which is a totally synthetic material. Pretty much unique in the organic chemistry world, PUS can be made to do any job from cushion and seats through to shoe sole, electrical insulation and even artificial heart valves. For our application it’s the compressible nature of PUS that makes them so appealing. By careful chemical manipulation varying sorts of foam can be made but it gets even better. Smart guys like Phil Turner at P&K Seating can inject a given grade of PU into a sealed mould carefully gauging just how much to ‘over inject’. By adding precisely the correct volume the size of the air bubbles is controlled which in turn dictates the level of compressibility and thereby comfort. Smart eh? The closed cell structure of Pu-based foams also resists water absorption and transfer meaning you’re not sitting on a large wet sponge.