Stage 1: Polychloroprene Chips
The first stage in the production of Yamamoto limestone neoprene is to make the polychloroprene rubber chips. As described in the introduction to neoprene, these are made through a chemical reaction using chloroprene. It is chloroprene that binds all the molecules of the reaction together, leaving us with polychloroprene chips. Oil-based methods use butadiene derived from petroleum to do this, while Yamamoto uses acetylene derived from the calcium carbonate found in limestone.
To do this, extracted limestone is fed into a furnace and heated at a temperature around one-tenth of that used for refining petroleum. The source of the heat is from burning used tires and hydroelectric power sourced from several local dams (any waste heat is then reused to power a local eel nursery). From the furnace, components are reacted with other chemicals to make the acetylene gas needed for the chloroprene rubber chips.
The next process—polymerization—is similar for both oil-based and limestone-based methods, and both achieve the same results (albeit with different ingredients). At this stage what is produced is not that different in terms of strength and insulation. However it is the next stage of the manufacturing process that gives limestone neoprene its micro-cell advantage.
Stage 2: Baked in the Oven
The next stage is the creation of a neoprene sponge block—similar to baking a loaf of bread, but much larger. The polychloroprene rubber chips are melted and mixed together with foaming agents and black carbon pigments, and then baked in an oven to make it expand. It's during this process that Yamamoto's specialized technology combines with the calcium carbonate to create the micro-cell structure of limestone neoprene.
Once cooked, the sponge is cooled, leaving a big neoprene sponge block about 150mm thick and with a very high independent closed-cell structure of 94%—each cell filled with nitrogen gas.
Stage 3: Sliced into Sheets
Once this sponge block has cured the next process is to slice it up into sheets. Again, this is like slicing a loaf of bread, except it is slit horizontally and to the desired neoprene thickness, ie 2mm, 3mm or 5mm (or whatever thickness may be required). Because the thickness of limestone neoprene is measured before the nylon is added, it is a true indication of a wetsuits thickness (compared to many Chinese-made suits, which include neoprene and nylon in the measurement and end up being thinner than what they claim to be).
Each sliced sheet of foamed neoprene has absolutely no strength—at this stage it is easier to rip than a piece of paper! But even now its very high micro-cell structure gives it exceptional thermal insulation properties.
Stage 4: Laminated with Nylon
The last process is laminating the soft sheets to give them strength. High stretch nylon or polyester jersey knit is laminated to one side or both sides of the neoprene sheet, to make smoothie (neoprene with a single side of nylon) or double lined neoprene (nylon on both sides). The nylon jersey layer is very strong and gives the neoprene its strength and colour, and also allows it to slide over the body without sticking to the skin (like it would if it was a rubber or cell finish). It can also be lined with Titanium Alloy Alpha to make it even warmer.
The quality of the laminated bond between the nylon jersey and the neoprene foam is critical to strength and longevity. A strong bond will not degrade, blister or delaminate. This can be a major problem with any inferior bonding during manufacture.
The Result: Yamamoto Limestone Neoprene
What we end up with after these stages is super strong and highly insulated sheets of limestone neoprene, which are then shipped to Seventhwave, ready to be cut and constructed into a wetsuit!