Duct tape is one of the most versatile adhesives on the market today. Though originally used to hold duct work together, hence the name, duct tape is used for packaging, quick repairs and a variety of other everyday projects. But one question that many people have is whether or not duct tape, for all its usefulness, is safe to use at high temperatures, and how flammable it is.
The base of most duct tape is a cotton mesh fabric. The mesh fabric allows the duct tape to be torn in either direction, and the fabric adds strength to the tape, making it extremely difficult to break. The mesh fabric is flammable, but it is coated with other materials.
The cotton mesh is then coated in polyethylene. Polyethylene is a synthetic material that is flexible enough to allow the cotton mesh to move, but which protects the fabric from all sorts of damages. These include fraying, moisture and heat. The polyethylene coating is not flammable, even if the cotton mesh fabric underneath it is.
The last component of duct tape is the adhesive. The adhesive used for duct tape is unique, being formed from rubber compounds which form a much stronger bond than that used for other varieties of tape. In addition to being a strong bonding agent, though, rubber is not flammable, which means that the adhesive on duct tape is safe from fire.
Duct tape is recommended for use in temperatures between 20 and 200 degrees F. While the tape is not flammable, the extremes of temperature will make it difficult for the rubber adhesive to properly bond with a surface that's too hot. The same is true for bonding with materials at a lower temperature, since it may lead to difficulty bonding and keeping that bond when the temperature rises.
In order for duct tape to be sold on the open market, it has to meet certain standards of safety. One of those safety standards is that duct tape must be shown to be nonflammable and to be safe to use on ducts that might heat up significantly.