Once the frame is built, and the ground is smooth, felt can be installed. I could easily attach it to wooden panels using screws. On the walls, I used silicon, which may not remain for long, but water pressure will keep it in place. Felt is a cheap material and can be found in garden centers.
The liner on another hand, is quite expensive. I chose one made of EPDM rubber (ethylene propylene diene monomer); it is cheaper and stronger than rubber, and cleaner than PVC. I asked for the help of another person to pull the liner. Both people move at the same pace on each side of the structure. It took about an hour to position the liner properly. There were a lot of folds at the beginning, and some remained because of the shape of the pond. One has to make sure that there is enough material on all sides, before pouring some water.
I used rain water from a collector. Water must be poured slowly, because it pushes the liner against the wall and it needs to be repositioned carefully.
I used weights (stones) to prevent some areas from moving the wrong way.