I've got a whole bunch of these, more than I can ever possibly use, and would like to reclaim some storage space. PETE is the most oxygen-impermeable plastic I know of, and is the same material used to make soft-drink bottles nowadays. I'm not sure what the caps are made of, probably HDPE, but they're quite thick so provide a good oxygen barrier as well. Both sizes are square and take up less shelf space than a round bottle comparable volume. 30 x 500ml bottles, $10 plus shipping per half-dozen, $40 plus shipping if you take them all. 23 x 1000ml bottles, $15 plus shipping per half-dozen, $50 plus shipping if you take them all. If I find that 24th 1000ml bottle I'll toss it in. It's probably not worth the money to ship these outside the US, but I'm game if you are.