Foil, Semi-Rigid, or Smooth Metal? Dryer Duct Materials, Explained Honestly
Stand in any hardware store's venting aisle and you will find four products that all claim to be dryer duct: white vinyl coil, shiny ribbed foil, semi-rigid aluminum, and lengths of smooth rigid metal pipe. One of those is a fire hazard, one is misused in most homes that have it, one has exactly one legitimate job, and one is what the entire concealed run should be made of. Since the difference is invisible once the wall closes up, here is the honest material guide.
The ground rules the code sets
The mechanical code our villages have adopted — Skokie, for example, runs on the 2021 International Mechanical Code per its current building codes page — is specific about dryer exhaust. Concealed ducts must be smooth-interior metal, joints must run in the direction of airflow, and fasteners may not protrude into the airstream: per the IMC's exhaust systems chapter, screws sticking into the duct interior are prohibited, because every protruding screw tip is a lint hook. The code also caps total run length, with deductions for every bend. None of this is bureaucratic fussiness; each rule exists because lint accumulates at exactly the features the rules prohibit.
White vinyl coil: remove it, full stop
The white plastic spiral duct sold for decades as "dryer hose" is combustible. It softens with heat, sags into lint-collecting bellies, and if lint ever ignites, the duct itself joins the fire. It has been out of code for concealed and transition use alike for many years, but our housing stock predates that by decades, and we still find it behind dryers and, worse, inside walls. There is no maintenance schedule that makes vinyl acceptable. If any part of your run is white plastic, replacing it outranks cleaning it.
Ribbed foil: the misunderstanding in most laundry rooms
The shiny mylar-foil accordion duct is everywhere because it is cheap and bends around anything. Its problems are structural: the ribs that make it flexible also make its interior a lint ladder, it crushes if the dryer gets pushed back an inch too far, and a crushed section chokes airflow permanently. Foil's only defensible use is as a short, fully visible, listed transition connector — and even there, semi-rigid does the same job better. What foil must never be is concealed: run through a wall, floor, or ceiling cavity, it fails both the letter of the code and the logic behind it. When we open up mid-century homes for repairs, concealed foil is one of the two findings we see most, along with crushed sections behind the machine.
Semi-rigid aluminum: one job, done well
Semi-rigid aluminum — the corrugated but self-supporting metal duct — exists for the transition: the short, visible hop from the dryer's outlet to the wall connection. The code allows listed transition ducts up to eight feet, never concealed, and semi-rigid is the right material for exactly that stretch. It holds a curve without collapsing, tolerates the occasional bump, and its corrugations matter less over a short visible run you can inspect. The failure mode is scope creep: semi-rigid sold by the coil gets stretched into 15-foot runs through floor cavities, where it becomes foil's problems in slightly better armor. Transition only.
Smooth rigid metal: everything else
From the wall to the outdoor termination, the answer is smooth-interior rigid metal pipe, joined without protruding screws and sealed without gaps. Smooth walls shed lint instead of holding it, rigid sections cannot sag into bellies, and metal contains heat rather than feeding a fire. Every rule of thumb about how often cleaning is needed quietly assumes a smooth-metal run; ribbed materials shorten those intervals badly. A dryer working through a smooth, sound duct also simply runs shorter cycles — the efficiency the ENERGY STAR program measures in the machine is only delivered when the duct behind it cooperates.
Why this matters extra in our housing stock
The near-north suburbs were built almost in one sitting — six in ten Niles homes went up between 1940 and 1969, and Skokie's median home dates to 1959. Household dryers were a novelty when those walls closed, so a large share of local runs were added later, with whatever material the installer had on the truck that decade. That is why we treat material identification as part of every cleaning visit: the duct's material and routing determine both the fire math and your honest cleaning schedule.
How to check yours in five minutes
Pull the dryer forward and look at the transition: white plastic means replace now; crushed anything means replace now; shiny foil means plan an upgrade to semi-rigid. Then find where the run enters the wall and where it exits outside. If you cannot account for the path between those two points, or the house has had laundry moved during a remodel, that concealed stretch is the question mark. We identify materials on every visit and quote replacements firm and in writing — if you want to know what is actually inside your wall, ask us to trace it.