High Temperature Flexible Duct: Complete Material Guide for 200°C+ Applications [2026]
Standard flexible duct fails above 70°C–120°C. If your application involves welding, engine exhaust, industrial ovens, or any process generating temperatures above 200°C, you need specialized high-temperature duct — and choosing the wrong material can mean equipment damage, fire hazard, or toxic fume release. Here's how to choose correctly.
When Standard Duct Materials Fail
Most facility managers and contractors default to PVC flex duct or aluminum flex duct because that's what they stock. These materials work fine for HVAC and general ventilation. But they fail — sometimes catastrophically — in high-temperature applications:
- PVC at +70°C: Begins to soften and deform. At +100°C it's structurally compromised. At +140°C it ignites and releases toxic hydrogen chloride gas. A PVC duct connected to a source above 70°C is a liability, not a solution.
- Aluminum at +120°C: The thin foil construction handles moderate heat, but repeated thermal cycling (heating and cooling each shift) causes micro-cracking and eventual failure. Aluminum also has zero chemical resistance to acid fumes, which many high-temp processes produce.
- Standard fabric duct at +80°C: Polyester-based fabric duct for HVAC dispersal is not designed for exhaust. The fabric degrades, stitching melts, and particulate accumulates in the porous material.
The common pattern: someone installs the wrong duct, it works for a few weeks, then it softens, cracks, or catches fire. The repair costs more than the right material would have cost upfront. We see this regularly with auto repair shops using PVC for tailpipe exhaust extraction.
High-Temperature Flexible Duct Materials Compared
Four materials cover the full range of high-temperature flexible ducting. Each has a temperature window where it's the best choice:
| Material | Temp Range | Construction | Best For | Approx. Cost |
|---|---|---|---|---|
| Silicone-Coated Fiberglass | -30°C to +300°C | Fiberglass fabric + silicone coating + stainless steel helix | Welding, engine exhaust, lab exhaust, ovens up to 300°C | $10–$25/ft |
| Stainless Steel Flex | -200°C to +650°C | Corrugated stainless steel strip, helically wound | Furnace exhaust, kiln venting, high-temp process gas | $20–$60/ft |
| Fiberglass (Uncoated) | -40°C to +500°C | Woven fiberglass with wire helix, no coating | Short-term high-temp exhaust, disposable applications | $5–$15/ft |
| Ceramic Fiber | up to +1,100°C | Ceramic fiber blanket over wire frame | Foundry exhaust, glass forming, extreme-temp processes | $30–$100/ft |
Silicone-Coated Fiberglass: The 80% Solution
For roughly 80% of high-temperature ducting applications, silicone-coated fiberglass is the right answer. Its +300°C rating covers welding (200°C–300°C at the extraction point), engine exhaust (150°C–250°C at the tailpipe), industrial ovens (up to 300°C), autoclaves (121°C–134°C), and laboratory exhaust with chemical resistance.
The silicone coating provides three things that uncoated fiberglass doesn't: chemical resistance (lab and industrial chemicals), moisture resistance (steam, condensation), and a smooth interior surface that reduces friction loss and resists particulate buildup. The stainless steel wire helix maintains the duct shape under vacuum (suction) and prevents collapse.
When You Need More Than Silicone
If your process temperature exceeds +300°C, silicone-coated fiberglass is no longer an option. Step up to stainless steel flex (up to +650°C) or ceramic fiber (up to +1,100°C). These are specialty products — significantly more expensive and harder to source. Common applications include furnace exhaust gas recirculation, kiln ventilation in ceramics manufacturing, glass forming off-gas, and foundry fume extraction.
For these extreme applications, we recommend consulting with our engineering team. The material selection depends not just on temperature but on gas composition, pressure, thermal cycling frequency, and duct run geometry.
Application-Specific Recommendations
Vehicle Exhaust Extraction (Auto Shops, Fire Stations)
Vehicle tailpipe exhaust ranges from 150°C (idling) to 250°C (under load) at the tailpipe tip. Silicone-coated fiberglass at +300°C provides a comfortable safety margin. Install with a loose-fitting extraction nozzle (not clamped tight to the tailpipe) to allow ambient air entrainment, which cools the exhaust stream and improves capture efficiency. Standard systems use 4"–6" diameter hose with an overhead rail or spring-loaded reel.
Welding Fume Extraction
Welding generates fumes at 200°C–500°C at the arc point, but by the time fumes reach the extraction hood (typically 6"–12" from the arc), temperature is 100°C–300°C. Silicone-coated fiberglass handles this range. Use 4"–6" diameter hose with a flexible extraction arm. Position the hood within 12" of the arc — capture efficiency drops to near zero beyond 18".
Industrial Oven & Kiln Exhaust
Oven exhaust temperature depends on the process: curing ovens run 100°C–200°C, paint bake ovens 150°C–220°C, and ceramics kilns 500°C–1,200°C. For ovens up to 300°C, silicone-coated fiberglass works. Above 300°C, use stainless steel flex or rigid stainless duct. Kilns above 650°C require ceramic fiber or rigid refractory-lined duct.
Laboratory & Testing Facility Exhaust
Labs present a unique combination: moderate temperatures (typically under 200°C) but aggressive chemical exposure. Silicone-coated fiberglass is the standard here because it provides chemical resistance that stainless steel doesn't — acid fumes corrode stainless steel over time, but silicone coating is inert to most laboratory chemicals. See our detailed guide: Silicone Duct Hose for Laboratory Ventilation.
Sizing for High-Temperature Applications
High-temperature duct sizing follows the same airflow principles as standard duct — but with one critical addition: you must account for thermal expansion of the air. Hot air is less dense, so you need a larger duct diameter to move the same mass flow rate compared to ambient-temperature duct.
Rule of thumb: for every 100°C above ambient, increase the duct diameter by one size (e.g., from 4" to 5"). This compensates for reduced air density and maintains adequate capture velocity at the source.
| Application | Exhaust Temp at Duct | Recommended Diameter | Airflow Range |
|---|---|---|---|
| Single vehicle tailpipe (car) | 150°C–200°C | 4"–5" (100–125mm) | 300–500 CFM |
| Single vehicle tailpipe (truck/diesel) | 200°C–250°C | 5"–8" (125–200mm) | 500–1,000 CFM |
| MIG/TIG welding extraction | 100°C–200°C | 4"–6" (100–150mm) | 500–1,000 CFM |
| Oven exhaust (curing) | 100°C–200°C | 6"–10" (150–250mm) | 500–2,000 CFM |
| Oven exhaust (paint bake) | 150°C–220°C | 8"–12" (200–300mm) | 1,000–3,000 CFM |
| Furnace exhaust | 300°C–650°C | 8"–16" (200–400mm) | 1,000–5,000 CFM |
Installation: What Changes Above 200°C
Installing high-temperature duct isn't the same as hanging standard flex duct. Several things change:
Clamps and Fasteners
Use stainless steel band clamps exclusively. Standard galvanized clamps off-gas zinc at temperatures above 200°C, creating toxic zinc oxide fumes. Worm-gear stainless clamps (SAE type) are the standard. Torque to manufacturer spec — over-tightening crushes the wire helix.
Tape and Sealant
Standard duct tape fails at +60°C. For joints up to +150°C, use aluminum foil tape. For +150°C to +260°C, use high-temperature silicone tape. Above +260°C, use fiberglass packing rope with stainless wire tie. Never use silicone caulk — it's rated for static applications, not for duct joints that vibrate.
Supports and Hangers
Support high-temperature duct every 3–4 feet (vs 6–8 feet for standard duct). The material becomes slightly more flexible at operating temperature, and unsupported spans will sag, creating low spots where condensate or particulate collects. Use stainless steel straps or cradles — nylon zip ties melt above 80°C.
Thermal Expansion
Silicone-coated fiberglass expands approximately 1% at +300°C. For a 25-foot run, that's 3 inches of linear expansion. Leave slack at one end or use an expansion joint. A duct installed taut at ambient temperature will pull connections apart when it heats up.
Clearance from Combustibles
Even though the duct material is self-extinguishing, the exterior surface radiates significant heat. Maintain at least 6" clearance from combustible materials (wood framing, insulation, wiring) for ducts operating above 150°C. At +300°C, increase to 12" or add a heat shield.
Need High-Temperature Duct for Your Facility?
We stock silicone-coated fiberglass duct hose in 2" through 16" diameters at our Houston, TX warehouse, with custom lengths available. Tell us your application and temperature range — we'll specify the right product and get you a quote within 24 hours.