Duct tape is unlike many other tapes in that its backing, also known as the "non-sticky" part, is made of cloth fibers. These fibers are usually composed of cotton. These cloth fibers result in duct tape having a very high tensile strength, protecting it from accidental rips or tears. In fact, it can be quite difficult to break a piece of duct tape unless you are tearing it horizontally or along the course of the fibers.
Duct tape uses a rubber-based adhesive. This adhesive is what allows the tape to remain stuck to a wide variety of surfaces. Duct tape's adhesive withstands moisture and harsh temperatures and will often stay sticky for much longer than traditional tape. It is worth noting that while duct tape can be used to seal ducts, periodic checks should be performed on the seals to ensure the tape has not lost its grip.
Duct tape is available in a wide variety of colors but is usually found in its traditional form, which is either a steel gray or black. Industrial-grade duct tape is usually the same color as the ducts it is used to seal. Duct tape appears ridged on the outside, with each tiny ridge marking one of the cloth fibers that compose the backing. On the sticky side, duct tape is usually white or light gray.