Flexible Ducting
Flexible ducting for ventilation, extraction and air movement, in diameters from 38mm up to 500mm. Whether you need insulated aluminium foil flex for a condensation-sensitive supply run, high-temperature silicone flex for hot air, anti-static PU flex for dust extraction or a general-purpose PVC hose, this range covers it — all from a Leicester-based UK supplier with stocked sizes despatched next day when ordered by 3pm.
Which type of flexible ducting do I need?
Aluminium foil flex — the standard choice for HVAC connections. Available insulated or uninsulated, in 10m lengths and 16 diameters from 80mm to 500mm. Use the insulated version to reduce heat loss and condensation on supply and extract runs.
Combi flex — combination flexible ducting in 6m lengths, 80mm to 500mm diameter, a versatile all-rounder for ventilation connections.
High-temp silicone flex — double-ply silicone flexible ducting in 4m lengths for hot air handling, from 38mm right up to 300mm diameter.
PU flex — anti-static, lightweight polyurethane flexible ducting from 80mm to 315mm, well suited to dust and shaving extraction.
PVC grey flex — economical grey PVC flexible hose in 14 sizes from 80mm to 500mm for general ventilation and extraction.
Semi-rigid flex — holds its shape once formed, supplied in 3m lengths from 100mm to 355mm diameter.
Hose clips — quick-release clips in four sizes securing flexible ducting up to 525mm diameter.
Matching flexible duct to rigid systems
All the popular spiral duct diameters are represented — 80mm, 100mm, 125mm, 150mm, 160mm, 200mm, 250mm, 315mm and more — so flexible duct can drop straight onto fans, grille boxes and spiral duct fittings without adaptors in most cases (use a male connector where flex meets plain spiral duct). Use a top hat spigot to break into a plenum, and secure every joint with a hose clip for an airtight connection.
Getting the best from flexible ducting
Flexible duct is at its best used in short, gently curved sections — connecting a fan to rigid duct, dropping from a plenum to a grille box, or absorbing vibration and minor misalignment between components. Keep runs pulled reasonably taut rather than compressed, avoid tight kinks, and support longer sections so the duct does not sag; every unnecessary ripple adds resistance the fan has to overcome. For long straight distances, rigid spiral ducting with a short flexible connection at each end usually gives quieter, more efficient results than an all-flex run. If the duct handles warm, moist air — bathroom or kitchen extract passing through a cold loft, for example — choose the insulated aluminium version to keep condensation from forming inside the duct.
UK mainland delivery is free on orders over £400 ex VAT. Lead times for any non-stocked item are shown on each product page before you order, and our Leicester team can help you pick the right flex type for the job.
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Aluminium Foil Flex
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Combi Flex
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High-Temp Silicone Flex
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Hose Clips
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PU Flex
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PVC Grey Flex
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Semi-Rigid Flex
What is Flexible Ducting?
Flexible ducting is a lightweight, bendable tube used in ventilation systems to connect components such as fans, grilles, and diffusers to rigid spiral or rectangular ductwork. It consists of a wire helix frame covered with aluminium foil, PVC, or fabric, allowing it to flex, bend, and compress for easy installation in confined spaces.
While flexible duct is extremely convenient for short runs and connections, it should not be used as a substitute for rigid spiral ducting on long straight runs. The corrugated inner surface of flexible duct creates significantly more air resistance than smooth spiral duct, increasing pressure drop and reducing system efficiency.
Types of Flexible Ducting
Aluminium Flexible Ducting
The most common type, made from multi-layered aluminium foil with a steel wire helix. Suitable for general ventilation, cooker hood connections, and bathroom extraction. Lightweight and easy to cut and install.
Insulated Flexible Ducting
Features an inner aluminium core wrapped in thermal insulation (typically 25mm glass wool) and an outer vapour barrier jacket. Essential for preventing condensation in systems where the duct passes through unheated spaces such as lofts, roof voids, and external wall cavities.
Acoustic Flexible Ducting
Designed to attenuate noise from fans and air handling units. Features a perforated inner liner surrounded by acoustic insulation that absorbs sound energy. Used in noise-sensitive environments such as offices, recording studios, and residential bedrooms.
Semi-Rigid Flexible Ducting
A middle ground between fully flexible and rigid ducting. Semi-rigid duct holds its shape once bent, providing a smoother internal bore than standard flexible duct. This reduces pressure drop while still offering some flexibility for installation. Commonly used in domestic MVHR (Mechanical Ventilation with Heat Recovery) systems.
Sizing and Installation
Flexible ducting is available in the same standard diameters as spiral duct (80mm to 500mm), ensuring compatibility with rigid ductwork systems. When installing, always:
- Keep runs as short and straight as possible — each bend adds significant pressure drop
- Fully extend the duct — never leave it compressed, as this dramatically reduces airflow
- Support with hangers or saddles at maximum 1.5m intervals to prevent sagging
- Seal connections with duct tape or jubilee clips
- Avoid sharp bends — maintain a minimum bend radius of 1.5x the duct diameter
Why Choose Alpha Air?
We stock all common sizes and types of flexible ducting for immediate dispatch. With many years in the ventilation industry, our team can advise on the right type for your application. Free delivery on orders over £400.
Frequently Asked Questions
How long can a flexible duct run be?
Flexible ducting should be kept as short as possible — ideally under 1.5 metres. Long runs of flexible duct create excessive pressure drop due to the corrugated inner surface. For runs longer than 1.5m, use rigid spiral ducting with flexible connections only at the ends.
Do I need insulated flexible ducting?
Yes, if the ducting passes through an unheated space such as a loft, roof void, or external wall cavity. Without insulation, warm moist air inside the duct will condense on the cold duct walls, leading to water dripping and potential mould growth. Insulated flexible duct prevents this.
What is the difference between flexible and semi-rigid ducting?
Standard flexible ducting is fully collapsible and has a heavily corrugated inner surface. Semi-rigid ducting holds its shape once bent and has a smoother bore, giving better airflow performance. Semi-rigid is preferred for MVHR systems and applications where lower pressure drop is important.
Can I connect flexible ducting to spiral ducting?
Yes. Flexible ducting slides directly over the male (crimped) end of spiral fittings or over a male coupler attached to spiral duct. Secure the connection with a jubilee clip or duct clamp and seal with foil tape for an airtight joint.