People have been confused about wearing neck gaiters (those tube-like garments that can be pulled over the mouth and nose) to Walt Disney World. Because of the confusion, Disney has directly addressed the issue. According to the Walt Disney World website;
At this time, based on guidance from health authorities, neck gaiters and open-chin triangle bandanas are not acceptable face coverings.
I saw people turned away at the Magic Kingdom for neck gaiters with ear holes, so don’t chance it. If you arrive with only a gaiter, you can buy disposable masks in a vending machine at the Transportation & Ticket Center.