Made of plastic. It’s fantastic. But what’s the point of preventing your lettuce going brown if you’re eating it straight away? I have to confess I rarely use it.
The times I do, however, it does make a difference. For example this saturday, at the barbecue, I made a huge salad that was likely to be too big. And then yes, the next day the lettuce was not that fresh but still looked quite ok. So I used it to fill burritos. Yummy!