Don't try to protect the polished surface by coating it with duct tape. That doesn't work. <img src="/images/graemlins/frown.gif" alt="" />

I am currently using this mirror card. It is about 2mm thick, which I figured was thin enough to include. It comes as a big A4 sheet which you can cut to the exact size you need for your PSK. It is waterproof and it burns, if you are desperate for tinder (a thin shaving lasts for about a minute). The reflective surface is mirror-like; it's covered with plastic film to protect it.

The drawbacks are that although it is quite stiff, it may not be as flat as a glass mirror would be. It'll be as good or better than the tin, though. I don't know how important flatness is to heligraphy. Also, there's no aiming hole. (I don't know how to use that yet anyway.)

Overall I am please with it. Much better than a polished tin. It's good enough to use as an improvised periscope, for seeing rather than signalling.