Lucca, I used a sewing machine, but hand sewing is perfectly doable. I use 8 inch squares of fabric X 3, joined top and bottom on wrong side, turned and a 1/4 in channel sewn along top for the wire, then pleated to approc 3 inches depth. Lastly I use a piece of fabric 2 x 4 to bind each raw edge, forming a channel for the elastic, which I knot and pull through to hide.
Here is a close-up of one. I use expensive (in this case Liberty) fabric for the front and cheaper plain fine cotton for the two inner layers.