I made my own hay nets out of baling twine, with openings that are about 2 inches square. The horses have to work a little harder to get the hay out; it takes them a lot longer to eat the hay I give them. They eat from the bag first, then vacuum up the scraps - we waste very little hay. There are a lot of designs for "slow feeders," some are as simple as a box you put the hay bale in, and a weighted frame with fence wire stapled to it that sits on the hay and goes down as the hay gets eaten .