Thanks mablo. I'll look for plastic cassetes; screw top sounds like the way to go to me, too.

Btw, I received an email from Roger Luo that he only has the "L" size these days. It's 58cm X 61 cm (so approx. 23x24" I guess). Is that a large enough bag? I'm quite intrigued by the fact that it is cotton, actually.

Cheers
Philip