The smoothie bowls itself is made of glass and the lid is made of plastic (polypropylene) with a silicone rubber edge to be able to close properly. You attach the lid by folding the edges, as it were, so that they snap into place. That is a bit of practice, because you still have to put some force and the lid can move. They are stackable by the way, also very nice. They can with lid and all in the freezer and in the dishwasher. Without a lid they can be put in the oven.
I have been using the glass storage boxes for a few months now and I am quite satisfied with it. The dramas with turmeric stains and fat layers are definitely a thing of the past; they are very easy to clean. The only thing I had to get used to is how immensely cold they get in the freezer.
Glass conducts well, so you must have frost-resistant fingers or grab the glass storage boxes with potholders or a tea towel, at least in the case of a -18 degrees freezer. They are also considerably heavier than plastic storage containers. That makes them less suitable for ‘just a snack in your handbag’. Stainless steel may be more suitable for this.