Ventilation duct materials decide whether an industrial or laboratory exhaust system survives its own chemistry, temperature, and mechanical duty — or fails and gets replaced. Most selection advice starts from a type list and stops there; this guide starts from your operating conditions instead. It compares nine materials — PP, PVC, CPVC, PE, PVDF, galvanized steel, stainless steel, aluminum, and FRP — across the properties that drive selection, then runs a five-step decision tree that narrows the field to one or two candidates. Scope: industrial process air, laboratory fume exhaust, and corrosive-air handling. Residential HVAC (flex duct, duct board) is a different decision and is not covered here. Every number is traced to a verified source; temperature values are service ceilings, not guarantees.
Key Takeaways
- Ventilation duct materials are the substances a duct system is fabricated from. Start with media, then screen temperature, mechanics, lifecycle cost, and certification.
- Pick by decision order, not by type lists. Each step narrows the next shortlist.
- PP is the mid-temperature corrosive-fume workhorse. Typical continuous service is ~90°C, grade/load-dependent; density is 0.90–0.91 g/cm³; it resists most acids, bases, and salts.
- Temperature ceilings change the shortlist fast. PVC ~60°C, PP-H ~90°C, CPVC ~93°C, PVDF ~135°C; all are typical, grade-dependent values.
- Galvanized steel brings stiffness, not corrosion immunity. Modulus is ~200 GPa versus PP’s 1.3–1.8 GPa, but wet acid attacks zinc and steel.
- The table and tree narrow the choice to 1–2 candidates. Final approval needs the manufacturer’s compatibility table and project spec.
Direct Answer: How the Choice Works
The short answer, by decision order
Ventilation duct materials are the substances a duct system is fabricated from, and the correct one is whatever survives your media at your temperature under your mechanical and budget constraints. There is no single best material: the same polypropylene (PP) system that suits a plating line would be the wrong choice for a wet-chlorine scrubber exhaust, where PVDF or FRP belongs.
The working order is media chemistry → temperature ceiling → mechanical and space constraints → lifecycle cost → certification and maintenance. A PP-H line around 90°C can stay in the thermoplastic branch, but the value is grade- and load-dependent. Each step outputs a constraint that narrows the candidate list before the next step runs. That is the frame: your conditions, run through the order, produce the material — and the rest of this guide is the evidence and numbers behind that decision.
Three families: thermoplastics, metals, composites
Nine materials sort into three families with different strengths and failure modes. Thermoplastics — PP, PVC, CPVC, PE, and PVDF — are often selected for aqueous chemistry, but their density is not one range: PP, PE, and PVC in this comparison span roughly 0.9–1.4 g/cm³, while CPVC and PVDF are left to grade data. They cap out at temperatures far below metals and are welded or solvent-bonded into homogeneous runs.
Metals — galvanized steel, stainless steel, and aluminum — bring stiffness (elastic modulus 70–200 GPa), fire safety, and wide temperature range, and their corrosion resistance is narrow and chemistry-specific. Composites — FRP — sit between: the resin matrix decides both the temperature ceiling and the chemical boundary. The families are starting points; the five-step tree in this guide does the actual screening, and by the end of this section you should know which family your duty falls into — corrosive aqueous chemistry (thermoplastics or FRP) or clean dry air (metals). After this module, choose the family that survives the media before comparing individual materials.
| Decision step | Carry-forward output |
|---|---|
| Media | Families that tolerate the stream |
| Temperature | Candidates with service headroom |
| Mechanics | Candidates that fit span, pressure, and space |
| Lifecycle cost | Candidates with defensible TCO direction |
| Certification | Final one or two candidates to verify |
What Each of the Nine Materials Is Designed to Do
Thermoplastics: PP, PVC, CPVC, PE, PVDF
Polypropylene (PP) is the corrosion-workhorse thermoplastic for mid-temperature fume duty: density 0.90–0.91 g/cm³ (about one-eighth of steel), continuous service typically around 90°C, and resistance to most acids, bases, and salts — with strong oxidizers and some organic solvents as the shared exception. PP duct is extruded or fabricated and hot-air welded into essentially seam-free runs, which makes it a common choice for plating, pickling, and laboratory exhaust.
Polyvinyl chloride (PVC) is the rigid economy option: density about 1.4 g/cm³, stiffer walls than PP, and a temperature ceiling around 60°C (140°F) — the main reason to reach past it. Chlorinated PVC (CPVC) extends that ceiling to roughly 93°C (200°F) with a higher heat deflection temperature (230°F), at higher cost, keeping PVC’s solvent-bonded joining (Corzan).
Polyethylene (PE) shares PP’s polyolefin chemistry with a narrower window — typically 60–70°C continuous — and is softer, which suits low-temperature budget runs more than corrosive fume duty. Polyvinylidene fluoride (PVDF) sits on top of the thermoplastic range: service from about −30°C to 135°C, resistance to strong oxidizers and wet or dry halogens, and a UL 94 V-0 flammability rating (Simtech) — a common candidate for semiconductor and aggressive reactive exhaust, at a higher cost than other thermoplastics.
Metals: galvanized steel, stainless steel, aluminum
Galvanized steel (GI) is carbon steel with a zinc coating, density about 7.85 g/cm³ and elastic modulus about 200 GPa — more than a hundred times stiffer than PP. That stiffness carries long spans, high negative pressure, and large diameters that plastics need heavy bracing to match. The limit is chemistry: in wet acidic or persistently humid corrosive service, the zinc layer and then the steel base are attacked, which is why GI belongs in clean, dry duct systems.
Stainless steel (SS) trades weight for corrosion control: density 7.9–8.0 g/cm³, corrosion resistance from a self-healing chromium oxide passivation layer (chromium at least 10.5% in the alloy), and 304 and 316 as the common duct grades — 316 adds molybdenum for better chloride and pitting resistance (Wikipedia). A melting range of 1325–1530°C removes temperature as a constraint in most ventilation duty. Aluminum (Al) is the light-metal option at about 2.7 g/cm³ — roughly one-third of steel — with a modulus around 70 GPa. Its protection is a surface oxide film that holds in atmospheric and neutral service but is attacked by strong bases and some acids (Wikipedia), so Al duct is a clean-service, weight-conscious choice, not a corrosive-duty one.
Composites: FRP
Fiberglass reinforced plastic (FRP) is a resin matrix reinforced with glass fiber, and the matrix sets the limits. Vinyl-ester systems are commonly cited around 250°F (121°C) — above PP, PVC, and PE — and chemical resistance varies widely by resin, which is why FRP selection always starts with a fabricator’s chemical resistance data sheet. Density runs 1.7–2.0 g/cm³, and parts are hand-laid or filament-wound, making FRP a heavier, specialist fabrication path than thermoplastics.
FRP earns its place in services that break thermoplastics: hydrofluoric acid, high-temperature corrosive fume, and large-diameter aggressive runs where metal would corrode and PP would not survive the temperature. It is a specialist choice — higher cost and resin-system expertise required — not a default. For a dimension-by-dimension deep dive on the four most common pairings, the four-material comparison on this site is the companion read. Choose a thermoplastic when the media and temperature fit its grade; choose metal for dry-service stiffness, or FRP when resin chemistry or temperature breaks the plastic envelope.
The Nine-Material Comparison Table
This is the working table for the ventilation duct materials comparison: nine materials scored across the dimensions that decide duct selection. Every number is traceable to the verified source ledger behind this guide; read the row for the property your project cares about, then read across to shortlist the materials that survive it.
How to read the table
Two conventions make the table safe to use. Temperature means continuous-service ceiling, not melting point — a thermoplastic softens and creeps well below its melt, so the ceiling is the number that matters for design. And every thermoplastic value is “typically” and grade-dependent: a specific PP-H or PVDF grade may rate higher or lower, and the fabricator’s data sheet for your grade supersedes this table.
Chemistry and cost follow the same rule. Chemical resistance is stated as a family boundary, not a guarantee at every concentration and temperature; cost is a direction (first cost versus lifecycle), never a price, because market and project variation make amounts misleading.
The nine-material comparison table
| Material | Density (g/cm³) | Continuous temp ceiling | Chemical resistance | Stiffness (elastic modulus) | Joining | Cost direction | Typical service |
|---|---|---|---|---|---|---|---|
| PP | 0.90–0.91 | ~90°C (grade/load-dependent) | most acids/bases/salts; not strong oxidizers | 1.3–1.8 GPa | hot-air weld / butt fusion | low-mid first cost; corrosion-duty TCO wins | mid-temp corrosive fume, lab exhaust, plating |
| PVC | ~1.4 | ~60°C (140°F) | most acids/bases/salts; not strong oxidizers | higher than PP | solvent weld | low first cost | rigid economy duct ≤60°C |
| CPVC | — (grade data) | ~93°C (200°F) | similar to PVC, higher temperature | — (grade data) | solvent weld | higher than PVC | hot corrosive air above PVC’s ceiling |
| PE | 0.94–0.96 | ~60–70°C | most acids/bases/salts; some solvents cause swelling | lower than PP | hot-air weld / butt fusion | often low first cost | low-temperature budget runs |
| PVDF | — (grade data) | −30°C to ~135°C | strong oxidizers, wet/dry halogens | — (grade data) | fluoropolymer weld | highest of thermoplastics | semiconductor, reactive/aggressive exhaust |
| Galvanized steel | ~7.85 | far above plastic limits | clean/dry service; wet acidic attacks zinc + steel | ~200 GPa | flanges / mechanical seams | low first cost in clean service | large spans, high negative pressure, dry air |
| Stainless steel | 7.9–8.0 | alloy/design-dependent; melt 1325–1530°C (not a service rating) | passivation layer; 316 better vs chlorides | ~200 GPa | welded / flanged | high | high-temp corrosive, chloride service, cleanroom |
| Aluminum | ~2.7 | far above plastic limits | oxide film; strong bases and some acids attack | ~70 GPa | welded / flanged | mid (above GI) | light clean-service runs, neutral atmosphere |
| FRP | 1.7–2.0 | resin-dependent; vinyl ester ~121°C (250°F) | varies by resin; HF service | high, direction-specific | resin-bonded / hand layup | high, specialist | HF, strong acids, high-temp corrosive |
Density and stiffness for CPVC and PVDF are left to the grade’s data sheet: exact values vary by formulation, and neither property is what selects these two materials — the temperature and chemistry columns are. After this table you can list the one to three materials whose density, temperature, and chemistry columns your duty survives — the shortlist the decision tree now screens.
Temperature and chemical limits at a glance
The temperature ladder is the fastest screening tool in the table. Standard PVC tops out around 60°C, PE around 60–70°C, PP-H around 90°C, CPVC around 93°C, and PVDF around 135°C — each “typically”, each grade-dependent. Metal duct sits far above all of them; FRP depends on the resin system, with vinyl ester commonly cited near 121°C.
Chemistry is where metals lose their temperature advantage. Galvanized steel fails in wet acidic service because both the zinc and the steel base corrode; stainless steel resists through its passivation layer, but reducing acids and high-concentration chlorides need a grade check; aluminum’s oxide film fails against strong bases and some acids. For aqueous acids, bases, and salts, the thermoplastics and FRP are the family to work from — and their shared exception, strong oxidizers, points toward PVDF or a confirmed specialty grade. Use the table to shortlist candidates, then choose only after the concentration-temperature pair is checked against the grade data sheet.
A Five-Step Decision Tree
The tree converts the table into a decision. Run the five steps in order with your own numbers; each step outputs a constraint that feeds the next. At the end you will have one or two candidates, plus the boundary conditions to confirm with a supplier.
Step 1 — Corrosive or chemically active media?
List the actual media in the exhaust: what it is, at what concentration, at what temperature. If the stream is aqueous acids, bases, or salts, the working family is thermoplastics and FRP — PP for most mid-temperature duty, PVDF or FRP for the aggressive edge. If the stream is clean, dry air with no corrosive chemistry, metals come back into play and galvanized steel is often the economical choice.
If the media contains strong oxidizers (fuming sulfuric, chromic), wet halogens, or hydrofluoric acid, no standard thermoplastic is a default — the candidates become PVDF, FRP, or a confirmed specialty grade, and the concentration-temperature interaction is exactly what the duct material for corrosive fumes guide on this site covers. Output of this step: the shortlist of material families that tolerate the media.
Step 2 — Temperature ceiling
Compare the maximum continuous exhaust temperature against the ladder: PVC ~60°C, PE ~60–70°C, PP-H ~90°C, CPVC ~93°C, PVDF ~135°C, metals far above, FRP resin-dependent. A system that runs at 65°C crosses out PVC and leaves PE marginal at its own ceiling; one that runs continuously at 95°C crosses out PP-H as well unless a higher-rated grade is confirmed.
Temperature is checked as continuous service, not occasional peak, and against the material’s ceiling, not its melting point. If the stream sits above every plastic’s practical range, the shortlist becomes metal or FRP, and this step hands that answer to the mechanical step below. Output: the candidates that survive the temperature column.
Step 3 — Mechanical and space constraints
Now apply the physical duty: duct diameter, run length, span between supports, positive or negative pressure, available headroom. Stiffness decides how much bracing a run needs — PP at 1.3–1.8 GPa versus steel at ~200 GPa is a difference of more than a hundredfold, so long plastic runs need closer supports, and large diameters under high negative pressure lean toward metal or FRP unless the plastic grade’s ratings are confirmed.
Weight and expansion belong in this step too: at 0.90–0.91 g/cm³, PP is about one-eighth the weight of galvanized steel per volume, which simplifies supports but introduces thermal expansion compensation on long runs (covered in the boundary section below). Sizing, velocity (industrial duct typically runs in the 5–10 m/s / 1000–2000 fpm band as a screening reference), and layout live in the duct sizing guide. Output: candidates that fit the mechanical envelope.
Step 4 — Lifecycle cost direction
Compare lifecycle cost, not first cost. In clean service, galvanized steel usually has the lowest first cost; PE is often low; PP sits in the middle; CPVC, stainless steel, FRP, and PVDF climb from there. Those directions reverse in corrosive service, where a cheap metal system can fail and require replacement while a thermoplastic system performs inside its validated service envelope — price per meter is not the decision variable.
The honest statement is a direction, not a number: first-cost directions are useful screening signals, but lifecycle rankings depend on your media, duty cycle, and replacement labor. Treat any price figure as project-specific and confirm by quotation. Output: the candidates whose lifecycle picture you can defend.
Step 5 — Certification, fire and maintenance
Check what the plant, insurer, or regulator requires: flame-spread ratings, fire-rated duct construction, pressure class, and the maintenance mechanism you can support. Standard thermoplastics are combustible; flame-retardant grades change the picture (UL 94 runs from HB to V-0, and PVDF is inherently V-0), but flame-retardant is not non-combustible — metal is the non-combustible path, while FRP is acceptable only when the specified resin/system meets the project fire classification.
Pressure class and maintenance belong here too. Ventilation ductwork is a low-pressure system, not a pressure pipe; if the duty exceeds the conventional ventilation class, confirm the grade and design or move to metal or FRP. Welded plastic runs need seam inspection and expansion maintenance; flanged metal runs need gasket checks. Output: the final one or two candidates that clear certification and maintenance — the input the boundary section and the worked example now validate.
When You Hit a Boundary: Fire, Pressure, Expansion, Upgrades
Fire-rated and pressure limits
The two boundaries that end most plastic duct conversations are fire and pressure. Standard thermoplastics burn; flame-retardant grades (the UL 94 HB→V-0 spectrum) slow ignition and flame spread but are not non-combustible. Where a project specification demands fire-rated duct construction, the practical path is metal unless a specified FRP system carries the required fire classification; a flame-retardant plastic grade only applies where the specification allows it.
Pressure is the second hard edge. Ventilation duct is a low-pressure airflow pathway, not a pressure pipe; plastic systems carry published negative-pressure ratings that are grade- and design-specific. If the duty exceeds the low-pressure ventilation envelope, confirm the rating against the material grade and design or move to metal or FRP. After this section you can decide whether your candidate needs a specialty upgrade or clears the boundaries as-is.
Thermal expansion and long runs
Plastics move with temperature in a way metals do not. PP’s linear thermal expansion coefficient is on the order of 0.10–0.15 mm/m·°C against steel’s ~0.012 mm/m·°C — roughly an order of magnitude apart — so a 30 m PP run at a 40°C temperature swing grows roughly 120–180 mm (about 5–7 in.) across its length.
Design must absorb that movement with expansion joints, bellows, or routing changes; without compensation, long rigid runs bow, stress joints, and pull hangers. Steel at the same duty grows roughly one-tenth as much, which is why long metal runs rarely need the same treatment.
When to upgrade to FRP, stainless steel or PVDF
Three upgrade paths cover the services that break standard thermoplastics. Strong oxidizers, wet or dry halogens, and reactive exhaust point to PVDF (service to about 135°C, halogen resistance, UL 94 V-0); hydrofluoric acid and high-temperature strong-acid duty point to FRP with a confirmed resin system; high-temperature chloride-laden streams point to stainless steel, with 316 preferred for pitting resistance.
The upgrade is a scope decision, not a reflex: each of these carries a higher specialist burden than PP or PVC. Confirm that the media exceeds the standard envelope in practice (using the Step 1 and Step 2 checks), then treat the upgrade as a specialist purchase — the fabricator’s chemical resistance data sheet and resin or grade selection are the working documents, not a general comparison. Use those documents to decide whether to keep the base candidate or issue an upgrade specification.
Worked Example: Choosing for a Real Exhaust Line
The scenario and inputs
A plating shop needs an exhaust line for a dilute hydrochloric acid pickling operation: about 10% HCl fume, maximum continuous temperature 70°C, design flow about 5,000 m³/h (roughly 3,000 cfm) through a 500 mm duct at about 7 m/s — inside the 5–10 m/s screening band. The run is 30 m horizontal, operates under hood negative pressure, and the plant wants the flame-retardant question answered in the specification. Budget is mid-range, and delivery matters.
The supplier-facing input set is:
| Input | Example value |
|---|---|
| Media / concentration | 10% HCl fume |
| Temperature | 70°C continuous |
| Flow / diameter | 5,000 m³/h; 500 mm |
| Velocity | 7 m/s |
| Run / pressure | 30 m; hood negative pressure |
| Certification / constraints | Flame-retardant review; mid-range budget |
Walking the decision tree
Step 1 (media): dilute aqueous HCl — an acid, not an oxidizer and not HF — so thermoplastics and FRP are the working family; galvanized steel drops from the default shortlist, while stainless steel still needs a grade check. Step 2 (temperature): 70°C crosses out PVC (~60°C) and leaves PE marginal at its own ceiling; PP-H (~90°C) survives with headroom. Step 3 (mechanical): 500 mm at 30 m under negative pressure is a PP candidate only with properly spaced supports and an expansion joint at mid-run; the 7 m/s velocity sits in the normal band. Step 4 (cost): PP has the defensible lifecycle direction against a metal option that does not clear the acid-compatibility check. Step 5 (certification): use a flame-retardant PP grade if the spec requires it and confirm the low-pressure ventilation class.
The output is PP, flame-retardant grade if specified, with expansion compensation on the 30 m run. Change the conditions and the answer moves: raise the temperature to 95°C and PP-H becomes marginal — confirm a higher-rated grade or step to CPVC or PVDF; introduce wet chlorine into the stream and PVDF becomes the candidate to verify; add hydrofluoric acid and the candidate becomes FRP with a confirmed resin. The method stays the same; only the inputs change. After the example you can run your own inputs through the same five steps and get a defensible candidate.
Common Selection Mistakes
The six mistakes and why they fail
Price and temperature mistakes are easiest to catch in a six-row pre-order check:
| Mistake | Immediate consequence |
|---|---|
| Price first | Corrosion can erase first-cost savings |
| Ignore temperature | PVC can soften or creep above its ceiling |
| Treat GI as corrosion-proof | Wet acid attacks zinc and steel |
| Equate flame-retardant with non-combustible | V-0 is not a fire barrier |
| Skip expansion compensation | Long runs stress joints and hangers |
| Use aluminum for corrosive exhaust | The oxide film can fail in strong bases or acids |
Use the table as a stop check: if a row matches the design, return to the relevant chemistry, temperature, fire, or expansion boundary before issuing the RFQ. Decide whether to stop the request or proceed only after the matching boundary is cleared.
What to Gather Before You Ask a Supplier
The six-item RFQ input list
A supplier can screen the material from six inputs. Map each field to the decision step before requesting a quotation:
| RFQ input | Decision use |
|---|---|
| Media and concentration | Chemistry shortlist |
| Maximum continuous temperature | Temperature ceiling |
| Flow and duct diameter | Size and velocity |
| Pressure and span / length | Mechanical envelope |
| Certification requirements | Fire and pressure path |
| Weight, headroom, delivery | Project constraints |
Confirm the working numbers against the manufacturer’s chemical compatibility table and grade data sheet — that document, not a general comparison, is the basis for the final material decision. For product scope, the site’s PP duct family is described across its pages as a 20–600 mm range: the general PP air duct page lists 20–500 mm reference sizes, while the PP Air Duct Guide and PP exhaust duct page describe the broader family up to 600 mm, including sheet-welded larger sections. The exact diameter, fabrication route, wall thickness, and grade are confirmed by quotation. The available forms include square tubing and flame-retardant duct. After this section you can assemble the six-item list that turns a vague inquiry into a screenable supplier request.
Related Products and Next Step
Where to go next
This ventilation duct materials comparison is the top of the material decision. Use the route below after the table and tree produce a candidate:
| Next decision | Continue with |
|---|---|
| Four-material comparison | four-material comparison |
| Corrosive concentration / temperature | duct material for corrosive fumes |
| Dimensions and layout | duct sizing guide |
| PP cluster overview | PP air duct guide |
Once the candidate material is fixed, the next step is specification and quotation: send the six-item list from the section above to a duct supplier, confirm the grade, ratings, and joining method against the project spec, and only then order. If the screen returns PP, inspect the product range for available forms; if it returns PVDF, FRP, or metal, use the same RFQ data with a supplier that offers that system. Prices and lead times come from a quotation with your specific inputs. Choose the next route from the table, then decide whether the supplier’s compatibility and project-specification checks support the candidate. That is the whole method — media, temperature, mechanics, cost, certification — and it applies whether you end up in PP, PVDF, metal, or FRP.
