They are more pressed foam than plastic. Plastic would shatter, these "tear" off more than anything. I have had them tear off very cleanly (if I can say that). So as far as gluing them back together, I didn't see too many pieces chip, most of the time, the blade would break when setting it down too hard. I am no longer landing the DF on the ground but in my hand so I don't break too many of them. Unless I fly indoors then the ground-based landings still happen.
Of course my rooftop crash oblitterated the entire set in a million pieces, but can't really say I've been going through blades lately
They are now taped where the blades are the narrowest and most likely to snap. This has helped me quit a bit in the confidence department.