Floppy disks, which are made from flexible plastic material, are also called

Floppy disks made of flexible plastic are also called diskettes.

Hard disks use rigid metal platters, not flexible plastic.

High density disks refer to storage density, not the flexible name.

Templates are document patterns, unrelated to storage disks.

The flexible mylar disc sits inside a protective plastic jacket.

Common diskette sizes were 5.25 inch and later 3.5 inch.