On some paper plates there is a coating of wax which is safe.
Although on most paper plates it's plastic and not actually wax although it appears to be wax.
Most paper food containers that appear to be coated in wax are actually coated with polyethylene (PE) plastic.
These containers are either made of fibers held together by a PE compound, or the container itself is lined with PE.
The PE serves as a moisture and gas barrier.
According to the U.S. Department of Agriculture (USDA), most paper products such as paper plates, wax paper, paper towels, and parchment papers are safe for use in the microwave.
However, brown paper bags, coffee cups, and newspapers are not sanitary and can emit toxic fumes.
In traditional paper plates and bowls, there is a plastic film that provides the oil and water resistance.
As eco-friendly plates are designed to eliminate the need for plastic, another material was needed to achieve oil and water resistance.