It’s really rather simple. Cotton is soft and non-abrasive. Polyester is not. While it’s true that polyester is useful for discharging static electricity, it can also create static electricity when it comes into contact with other surfaces (like the plastic used to create flat screen monitor frames). Cotton, however, is static neutral – it creates no static electricity. Period.
The outer face of a monitor screen is made from glass. Scratch it, and your stuck with a hard-to-view screen. Polyester is a nasty man-made product that’s fine for a dust cover, but it’s also abrasive. Monitor covers made from polyester can easily scratch your expensive monitor screen.
Cotton will not.
I don’t know what else to say, other than the shell of Monitor Bag padded covers are made from 100 percent soft, static-free cotton.