The better plastic shutters can perform equal to or better than stainless. Plastic shutters can be highly elastic and therefore return to their optimum shape after bending. They conform snugly to the shell without applying pressure to it. Static charge and debris on the plastic shutter does not seem to be an issue since the plastic shell has a much larger area. The most critical location for debris seems to be on the portion of the shell within the closed shutter.
Shutter motion can move such debris into the open head window and onto the surface of the diskette.
Shutter wear is also an issue if disks are to be inserted frequently. Although both aluminum and plastic are softer than stainless steel and are more susceptible to wear, diskettes do not normally experience a large number of insertions. Shutter wear is therefore not a consideration in most applications. Even the plastic shell can wear if it is inserted often enough. Shutter assembly processes are more important than the material itself.