The building code wants a UL 2158A listed duct. Your dryer manual may prohibit the thing that carries that listing.

Buy a duct that satisfies the code and the manual at once

This is the confusion at the center of dryer venting and it is worth understanding rather than guessing at. The IRC requires transition ducts to be listed and labeled to UL 2158A, in a single length not exceeding 8 feet, and not concealed within construction. Most manufacturers require semi-rigid metal and prohibit foil and plastic. The trap is that those two requirements do not overlap neatly: much semi-rigid duct carries no UL 2158A listing, and much of what does is foil. Since the code also requires installation per the manufacturer’s instructions, both apply. Aluminum-ribbon transition ducts sit in the overlap: metal, listed to UL 2158A, crush resistant, holding a full 4 inch diameter. Read the label for the listing and read the manual to confirm it is permitted.

Do not fasten duct joints with screws

The best detail on this page and the one that surprises people who have installed plenty of ducting. Sheet-metal screws are prohibited for dryer duct joints because the tips project into the interior and catch lint, which is the exact failure the whole system exists to prevent. The correct method is to crimp the male end into the female end in the direction of airflow and seal the joint with listed foil tape, with pop rivets on the outside of the joint acceptable in some jurisdictions. The same logic drives the code requirement that the insert end of a duct extends into the adjoining duct or fitting in the direction of airflow: nothing protrudes into the airstream, nothing catches, nothing accumulates.

White vinyl duct is prohibited, and it is still out there

If you pull a dryer out and find white plastic accordion duct behind it, that is the discovery of the day and it takes priority over the appliance you came to install. Flexible plastic and foil accordion duct used as the primary run is a code violation, vinyl burns more readily than foil, and both are prohibited by most codes and most manufacturers. This matters most in older houses and in rentals where nobody has looked behind the dryer in fifteen years. Replacing it is not optional maintenance, and the moment to do it is while the machine is already pulled out.

Rigid metal everywhere it is concealed

Anything running inside a wall, floor, ceiling or other concealed space has to be rigid metal, aluminum or galvanized steel, with smooth interior walls that neither restrict airflow nor collect lint. Flexible duct of any listing is not permitted there, and the transition duct specifically must not be concealed within construction. The reason is practical as much as regulatory: a flexible duct inside a wall cannot be inspected, cannot be cleaned, and will eventually sag or kink where nobody can see it. Where a bend is needed in rigid duct, use fittings rather than trying to persuade the pipe, and prefer long-radius sweeps.

Four inches, all the way, with no reductions

The minimum duct diameter is 4 inches and it has to stay 4 inches for the whole run. This is one of the strongest arguments against foil duct beyond flammability: its nominal 4 inch opening collapses toward roughly 3.25 inches in practice, and every inch of restriction is airflow the dryer does not get. The same goes for crushing. A dryer pushed hard against a wall flattens whatever is behind it, which is why the transition duct wants to be crush resistant and why a periscope-style rigid duct is often the right answer in a tight laundry closet where the machine sits close to the wall.

Measure the run against 35 feet, and count your elbows

IRC 2024 sets a default maximum equivalent duct length of 35 feet, and elbows count against it. That is why a run that looks short on a tape measure can still be too long: each bend adds equivalent length, and standard elbows cost more than long-radius swept ones. Some manufacturers give full credit for sweeps. If a laundry room is deep inside a house, this is the constraint that decides whether the duct can go where you wanted it to go, and it is worth calculating before cutting rather than diagnosing afterward from a dryer that will not dry. Support the duct at intervals not exceeding 12 feet and secure it in place.

The exterior cap must not have a screen

A specific and common mistake, usually made with good intentions. Screens are fitted to keep birds and pests out, and on a dryer vent a screen is precisely the thing that catches lint and blocks the outlet. The correct termination is a cap with a damper that opens under airflow and closes when the dryer stops, no screen, and positioned where the discharge is not going to be drawn straight back into the house. Once installed, this is the easiest part of the whole system to check periodically: run the dryer, go outside, and confirm the damper is open and air is moving.

Look for the listing on the label, and know what it says

Worth knowing because the packaging language is muddy. UL states that there is no such thing as "UL Approved" and that the term is not valid under any circumstances. What you are looking for is UL Listed to UL 2158A, which is a real listing earned by passing construction requirements plus tests for surface burning, flame resistance, bending, corrosion, puncture, impact and tension. Manufacturers frequently phrase their permission the same way, saying that only foil-type flexible ducts complying with Subject 2158A shall be used. Read the label rather than the marketing on the front of the packet, and keep the packaging until the installation passes.