I tried the old cotton batting-type Halloween spiderweb decorations once, and within an hour it was full of leaves and insects, but still hard to see from the sidewalk. I haven't bought it since. But Jaimie and Jay, the Wicked Makers, have found something much better. It's bigger, more visible, and reusable year after year!
Trenton Mills makes beef netting, and will sell you a five-pound roll for $30, and larger sizes if you need more. The stretchable fabric comes out to around 13 yards per pound, so that's 65 yards per roll. The company put up a Halloween page because so many people are using their beef netting for Halloween. It has an image gallery showing how others have used it in their home displays. Uncut netting can be used as an ethereal wrap for corpses or skeletons. Looks like fun, too!