Sheet polyester (Mylar) can be used as a non-adhesive support for mounting art in a mat.

A soldier’s drawing is kept in place with polyester half -moons. [Citation: Charles E. Kavenagh Collection
(AFC/2001/001/86254), Veterans History Project, American Folklife Center, Library of Congress]

• Half moons: Exhibits programs often use half-moons, or other rounded small polyester about ¼ to ½” wide that have a folded edge, to float art instead of using adhered hinges. (Half moons usually have a small piece of double-sided tape on the back to adhere them to the back mat). Artwork should be carefully evaluated for strength and stability before half moons are chosen as a mounting method.
• Polyester corners or edge strips: A folded piece of polyester can be used to support a sturdy piece of art, but beware sharp edges and be mindful of static charge. Sometimes sealing the edge that will be along the face of the work can provide a softer beaded edge than a cut edge.
• Encapsulations: Encapsulating the work of art may be desirable if this is compatible with the item. Often line or dot welds made with an ultrasonic sealer are used to keep the item carefully in place. The sleeve can then be taped or cornered into a mat. This is especially useful when creating a double-sided mat, where the polyester provides superior protection and allows the sleeve to be taped securely to the back window mat. It also allows pieces to be floated without adhesive hinges even if they are very delicate or thin. You may wish to include a sheet of buffered paper behind the item in the sleeve for long-term preservation.
• Polyester can be used as a simple slip sheet & to protect the surface of the art while it is being viewed. This is especially useful for items that may be brought out frequently (it will protect the artwork from the small amounts of saliva created when people talk in close proximity to the art). You can attach a sheet of polyester to the inside of the window mat, or attach it near the top of the back mat, allowing it to hang over the artwork (you can add a small ridge of polyester to the bottom for it to slot into for extra security), or you can simply lay a sheet of polyester on top of the art that fills the entire mat (so it doesn't slide).

Examples

View of Taped-in Encapsulation