This tape is essential for joining the frothing nozzle to the steam wand during any routine cleaning of your espresso machine. If you read our article on Cleaning an Espresso Machine, you'll see that you should take the nozzle off of the steam wand routinely so that you can clean both of them (the nozzle itself, and the steam wand) to keep them clear and free of rancid milk.
While this is called "Tape" is not an adhesive; it's a protective film that wraps around the threads on the wand of your espresso machine to make the nozzle easier to remove, and to make the seal air-tight. Wrap about an inch of it (even less) around the threads, and then put the nozzle back on the espresso machine. It's very easy to use!
Thread seal tape is used to seal pipe threads. It is sometimes called "plumber's tape," or "PTFE tape," or "tape dope." Many also call it "Teflon Tape." In fact, Teflon is not a material; it's simply a Brand Name owned by DuPont. But over time, this tape has been mistakenly referred to as "Teflon Tape" by many people.
Actually, this tape is not sticky. It's a polytetrafluoroethylene film (which is where "PTFE" comes from) that was made to wrap pipe threads. See the inset photo with this film wrapped around the end of the pipe. If you enlarge the image, you'll see the pipe threads through the film.
The function of this "tape" is to reduce friction (so that threaded pipe can be easily screwed together) and to form an airtight seal. Also, since it forms a film between the two pieces of pipe that are fitted together, it prevents the pipes from adhering to each other (because of oxidation and thermal cycling). This makes it EASIER to service the joint, i.e., easier to unscrew it later.
Therefore, it is used a lot in plumbing fixtures on water lines, where the object being threaded is to be serviceable and replaceable (like a shower head). The tape is wrapped around the exposed threads of a pipe before it is screwed into place. The tape is commonly used commercially in pressurized water systems, such as central heating systems, as well as in air compression equipment and thread joints with coarse threads, exactly as on any espresso machine.
One of the defining characteristics of PTFE is how good it is at defeating friction. The use of PTFE tape in tapered pipe threads performs a lubricating function, which more easily allows the threads to be screwed together, to the point of deformation, which is what creates the seal. This is an essential substance for cleaning and reassembling your frothing wand. It will maintain the life, and optimize the performance of your espresso machine.