I got type 1 trays (see photos) from my dentist, and later discovered that type 2 trays can also be used for teeth whitening. (As it happens, I have type 2 trays anyway to hold my teeth in place at night.)
The teeth whitening gel is expensive, and I wonder whether type 1 trays waste it, as most of the get that is in the dips is not coming into contact with teeth. I'd be grateful to hear other people's experiences of which type of tray they find effective.