Floating row covers are specifically designed to allow air & water thru. I can't say the same for your nylon or polyester drapes. I think your plants would smother/rot.

The floating row covers available commercially are made from sythtetic fabric and are meant to keep pests away fromt the plants. If you wanted to you could use the same material shear draperies are made from as floating row covers since any similar fabric would allow air and water through and keep insects away. You could probably even use fiberglass window screen.

You want to make sure whatever you use has a fine enough thread count so prevent the entry of the smallest insects. The commercially manufactured products do that successfully. Plus, you don't want anything that will eliminate LIGHT! Drapes, screens and other options will greatly reduce the amount of sunlight for your plants.

Yes - I forgot about sunlight. Commercially manufactured row covers are made specifically to allow maximum amounts of sunlight in. In fact, they're actually rated for it. The insect-weight type I purchase allows in 90% of sunlight. Some of the heavier-weight ones meant more for frost protection let in less.

Drapery fabric - including sheers - are meant to exclude a certain amount of sunlight to protect your household interior from fading as well as thermal conservation.

Sorry, but these products are NOT meant for use as insect row covers during the growing season - although in a pinch you might get away with using some of them for frost protection.

They have worked very well as floating row covers in my garden without resticting light any more than the commercial covers do (I have compared them side by side). While the commmercial types will last several years the difference in cost, if the shears are free, is worth getting the shears.