The big store ones we saw were.

I have also seen inkjet cartridges that have water proof ink in them, and paper that was Tyvek. I once bought a ream of it and printed some 8 X 10 charts to put on a clipboard in the cockpit. I was running a copy of Fagui on my Palmpilot at the time and it could print parts of charts. I was never very happy with it.

I did download, and print double sided, a couple of the NOAA BookletCharts for our cruise in the SF Bay area last summer. They worked well for the size, but nothing like a full (or 3/4) size chart.

Greg