This article is from the Sea Kayaking FAQ, by Todd Leigh with numerous contributions by others.
Plastic is heavier, more resistant to damage, harder to repair.
Fiberglass is lighter, easier to repair, results in finer lines, but
is more expensive. Fiberglass is generally more rigid than plastic,
which can result in a faster boat.
Wood is labor intensive but relatively easy to build (a little less
labor intensive if built from a kit), light, easy to repair, needs
maintenance. There are also a few companies that manufacture
wood/epoxy-construction kayaks, but they tend to be more expensive.
Fabric is labor intensive to build though a little less so than wood,
fragile, and needs maintenance.
Folding boats are a form of fabric boat that collapses for
transport/storage. They are generally more expensive to buy than any
other kind of boat, but there are other considerations that may make
them a better overall value. See section 5, folding kayaks, for more
information.
Inflatable boats tend to be much less expensive than any other sort of
boat.
Rigid boats may perform better than folding or inflatable
boats. Folding and inflatable boats have the advantage of easier
portability and storage. If you plan to travel with your boat, a
folding or inflatable boat will be easier to get on airliners. If your
home is tight on storage space, a folding/inflatable boat will be
easier to store than a rigid boat.
More exotic materials (like kevlar, carbon fiber) tend to be lighter
and costlier.
 
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