Leather + fabric.
One of the vendors has a fine strop for which you can
order replacement bits for a very fair price should you
cut it badly.
The ability to replace part of the strop has value if you get serious
about honing has merit ... While not commonly needed day to day a
pasted strop can put a final polish on a razor that will last
a long time. Just replace the canvas with pasted canvas
when honing and then replace with the clean fabric for day in day
out stropping.
One of the vendors also has a fabric and felt strop
for those that want a pasted strop handy.
Do get a quality strop. Note that you strop a razor each time you use
it so a strop gets used a lot and is as important as the quality
of the steel (Not expensive - quality).