I looked at a couple of pictures from the dataset posted above, and I think for the best effect the holes need to be local (so there's a regular / smooth surfac

I looked at a couple of pictures from the dataset posted above, and I think for the best effect the holes need to be local (so there's a regular / smooth surface, and only some of it is covered in holes), they need to be large enough to actually see individually and there needs to be some space between them (so meshes etc. don't work at all), and ideally they are also slightly irregular. You really don't encounter something that satisfies all of these naturally very often. Pretty much never. But it doesn't have to be "biological", it can be bread or plastic or anything else.