Method for bending: the large size does not make the case, but with a little practice it can be done quickly.
In fact there is not a folding but with a twist: you have to create a twist to create an inner circle (Ok it does not seem obvious)
Another unorthodox method:
1) First, fold the circle in 2: this takes the form of a banana
2) bringing the two ends of the "banana" by folding one over the other, adapt a little by turning to form a beautiful circle and here !!