Duct tape is a must-have household item that is reputed to be able to be used for repairing anything. What’s the old saying…if the duct tape is not working, you’re not using enough? Well, it turns out that this beloved adage is definitely funnier than it is true.
In fact, one of the main limits of duct tape is that it cannot actually be used on ducts. This is due to the way the tape’s adhesive responds to heat and cold.
Duct tape does not withstand high or low temperatures. Above 140 °F, the adhesive on the tape will melt. The tape itself can deform, even at a lower heat. Below 40 °F, the adhesive becomes brittle and loses its tackiness.
What Is Duct Tape Made From?
Duct tape has a simple yet effective design that consists of three layers. The first outer layer is made of polyethylene, a type of plastic that is derived from petroleum, giving it its water-resistant characteristic.
The second layer is made from a thin mesh cloth called cotton duck cloth, which strengthens the tape and makes it easy to tear without scissors. This layer is coated onto the polythene layer.
The third layer is an adhesive made up of a synthetic rubber compound called Styrene-butadiene.
This adhesive is a pressure-sensitive adhesive and uses the principle of van der Waals forces to adhere to the substrate. It is very strong, and thick coatings are applied for maximum adhesion, unlike regular scotch tape.
The adhesive has a fluid elasticity characteristic that allows it to withstand stress, which makes it a very sought-after product to use on household repair jobs.
Effects of Heat on Duct Tape
If you apply your tape to a repair that may heat up, you need to be aware that the effectiveness of the tape will not be great at all. In fact, it may completely fail.
If the surface that has been taped or the environment surrounding the tape reaches high enough temperatures, the adhesive on the tape will become less tacky and sticky and will basically just peel off.
Duct tape cannot handle temperatures that reach more than 140 °F.
At this temperature, the polymer bonds of the rubber adhesive (giving it its viscoelasticity characteristic) break, and the adhesive begins to soften.
If temperatures reach or exceed 140 °F, the plastic polyethylene layer and the rubber will start to melt but not burn.
Even though the cloth mesh layer is flammable, it is unlikely that the tape as a whole will catch fire. Instead, it is more likely to deform from the heat. This warping will also compromise the flush seal.
Hot air may also cause the adhesive to dry out over time, making hotter temperatures, even if they are lower than 140 °F, detrimental to the continued functioning of duct tape.
The limitations of heat resistance in duct tape make it unsuitable for electrical work, even though it is relatively non-conductive.
Effects of Cold on Duct Tape
As previously mentioned, it’s the viscoelasticity of the adhesive that gives the duct tape its strong stickiness or tack.
Once this synthetic soft rubber (a mix of both liquid and solid components) is exposed to temperatures below 40 °F, it reaches a point at which the rubber transitions from a flexible-like state to a solid glass-like state.
This causes the liquid part of the rubber to harden, reducing the contact forces between the adhesive and the substrate. Instead, you end up with an adhesive that is dry and brittle and no longer sticks to anything at all.
Let’s not forget the effect on the other layers of the tape.
When exposed to such low temperatures, just like the adhesive, the polyethylene layer also hardens. However, there is not much of an effect on the cloth mesh layer.
What This Means for Application of Duct Tape
While it might be tempting to use standard duct tape on everything because of its versatility, it is not designed to withstand extreme temperatures and cannot be used for everything.
It may be appropriate to be used to hold crafts together and aid in minor and/or temporary repairs, but it is not suitable to use on ducts that carry cold and hot air, which are pretty much all ducts.
If common duct tape is used on ducts and it fails, you run the risk of cold and hot air that has been conditioned leaking from the gaps that were meant to be sealed with the tape in the first place.
Your HVAC system will have to put in double the amount of effort to replace the lost air, which leads to more energy being used, as well as a hefty bill.
Malfunctioning tape can also lead to dirty air (containing dangerous gases from appliances like gas dryers and heaters) infiltrating clean air through leaks in the ducts because of the negative air pressure created.
This mixture of clean and dirty air then circulates your home, compromising indoor air quality.
Specialized Duct Tapes Are Available
Luckily, not all hope is lost. There are more suitable tapes out there that are designed for use with extremely high and low temperatures.
If you are unsure of what tape is best to use, always make sure that have been UL listed (should be on the packaging) and approved for ductwork or temperature-sensitive repairs.
A common specialized tape best suited for HVAC systems is foil or aluminum tape. It is made with lead, copper, or aluminum backing instead of polyethylene backing.
It is also coasted with an acrylic adhesive, which contains acrylates that withstand extreme temperatures.
Unlike duct tape, foil tapes do not have a cloth mesh in the middle layer and are only comprised of two layers (the acrylic adhesive and the metallic backing).
Foil tapes will also not melt or lose their integrity as metal, in general, has a very high tolerance for heat and will not be affected.
For packages that are going to be shipped, you should use packaging tape. UPS and FedEx will not accept your packages if you use duct tape.
For microwave use, you can purchase cellulose or freezer tapes.