The case material is soft plastic and one of the two I purchased does not close properly. My wife always uses an elastic band for insurance against the lid popping open and the bobbins falling out. So they should do the trick.
Such an excellent bobbin organiser! All my spools are well stored now. The lid has a good lock, the box stays closed at all times. Super fast dispatch to London. I'm over the moon with my purchase! Thank you very much, Seller!