Backing Tape, is also sometimes called Framing Tape, or Framers Tape,

Backing Tape is a specialty tape, used during the picture framing process to seal the back of the framed item. Although other types of adhesive tape may be seemingly be used, Backing Tape is used by framers because it is made of a material and adhesive that will not undermine the framed object or easily deteriorate over time.

It is important to seal the back of a framed object, as it prevents, atmopheric conditions effecting the object, it also prevents dust and generally insects from entering the inside of the frame.

Backing Tape can be purchased from any Framing Supply Store.