Is it linear or crosslink or super linear poly?

Recent discussion on repairing a split kayak with caution that linear can be welded and cross linked not, got me wondering - How do you know? I realize a manufacturer might identify which, but is there a definitive method (outside of a high tech materials lab) to ID material as to plain linear low density polyethylene, or cross linked or now super linear?

I would call the manufacturer. I believe nearly all polyethylene boats these days are linear poly (specifically super-linear poly), but I could be wrong. Jackson Kayak was actually one of the last makers of plastic whitewater kayaks to switch from cross-link to linear. Here is an article from EJ on why he stuck with cross-link so long:

Back in the very early days of rotomolded whitewater kayaks, nearly all were cross-link PE. Back then boats made of linear PE were much less stiff and did not seem to be as strong. But Perception had pretty much switched to linear PE by the early 1990s. Dagger offered boats in either cross-link or linear PE well into the 1990s.

Back then, Dagger’s cross-link kayaks were all multi-color swirl patterns and the linear boats were solid colors, or maybe I have that backwards.

If you have an older PE kayak and can’t get the information from the manufacturer based on the HIN and you really need to know you can take a small shaving of material from the inside of the cockpit rim. Heat it with a propane torch. If it melts, it is linear. If it holds its shape but sparks, and then catches fire, it is cross-link.

Necky when in Canada used cross-linked in their poly SOTs identified by black flecks mixed in.
I was lucky enough to have one.
I understand one drawback to cross-linked is that it is non recyclable but now very little poly from kayaks is being recycled anyway.