This spider web is made from a product called Beef Netting, which is usually used to cover sides of beef. It’s been appropriated by Halloween decorating enthusiasts because it makes great looking spiderwebs. You just stretch it out and cut holes in it. It can be dyed different colors if needed. Many haunters dye it with Rit brand fabric whitener, which makes it glow under UV light.
I bought my beef netting years ago from online store which is currently out of business. But you can get it directly from Trenton Mills, although the smallest amount is a 5 lb roll.