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we refer to it as consumers would, as a broad category. Actually there are different formulations, some of them proprietary. Out in the marketing world it all gets under the same tent.
I just googled royalex and found this info in the Paddler's Dictionary, which states that
Royalex is often mistakenly called ABS:
Royalex A laminate made of at least five layers of plastic used primarily for open canoe hulls. (Often incorrectly referred to as ABS.) An inner core of ABS foam is sandwiched between two or more layers of solid ABS sheeting and coated with outside layers of vinyl. It is very rugged and very heavy. Lighter weight versions are available that sacrifice some durability. The outer vinyl layer makes the hull slide well over rocks, but it is not very abrasion resistant, and a little of the surface peels of each time it glides over a rock. Also, fastening outfitting to the slippery hull is tricky.
end of quotation
the Hurricane kayaks are sheet molded of Trylon w. no intervening cores and no vinyl.
The vinyl coating on the outside of Royalex is for cosmetic purposes and for protecting the ABS substrate from UV degradation. The vinyl lining on the inside of Royalex hulls is to facilitate bonding D rings and such to the hull, and again, to protect the ABS substrate from UV degradation. In both cases, the vinyl layers contribute nothing to strength and would not influence whether or not the hull was susceptible to deformation.
The rest of the Royalex sheet is ABS. It is not solid ABS but it is ABS nonetheless. The foam ABS core is generated during the thermoforming process of constructing the sheet.