Insulated Flexible Ducting – The Right Duct for Every Job
If you're planning a ventilation project — whether that's a single bathroom extractor fan or a full commercial HVAC installation — choosing the right ducting makes all the difference. And once you understand what insulated flexible ducting brings to the table, it's hard to go back to anything else.
We've put together the right set of parts that, when installed correctly, ensure your ventilation system performs the way it should — for years to come.
What Is Insulated Flexible Ducting?
Think of it as a ventilation pipe with a built-in thermal jacket. At its core, it's a flexible, wire-reinforced inner duct — just like standard flexible ducting — wrapped in insulation (usually fibreglass or foam) and finished with a tough outer jacket.
That insulation layer does two really important things:
- It keeps heat in. Warm air travelling through a standard duct loses heat quickly, especially in cold loft spaces or external walls. Insulated air ducting keeps that warmth where it belongs — inside the duct and heading to where it needs to go.
- It stops condensation from forming. When warm, moist air meets a cold duct surface, condensation forms. Over time, that leads to dripping, mould, and potential water damage. Flexible insulated ducting eliminates that problem by keeping the duct surface temperature stable.
Whether you're installing ducting insulation for a home project or require insulated air ducts for a large commercial build, the benefits are exactly the same.
Picking the Right Size Insulated Flexible Ducting — Keep It Simple
Getting the diameter right is one of the most important steps. Here's a quick guide:
- 100mm insulated flexible duct — The go-to size for most domestic applications. Compatible with the vast majority of bathroom fans and standard kitchen extractors. If you're not sure, this is almost certainly the size you need.
- 125mm & 150mm — Used for higher-output fans, larger kitchen hoods, and light commercial applications.
- 200mm and above — Typically for commercial HVAC systems, industrial ventilation, and air handling units.
Always check your fan, the outer air valve, or the unit's outlet size before ordering. It's a two-second check that saves a return trip.
A Few Simple Tips to Get the Best Results
You don't need to be an expert to install insulated flexible ducting well. Just keep these things in mind:
- Shorter runs work better. The longer and more complex the duct run, the more resistance to airflow. Keep it as short and straightforward as possible, and your fan or system will work much more efficiently.
- Support it properly. Flexible ducting can sag if left unsupported over longer distances. Fix it every 1–1.5 metres to stop sagging, which can restrict airflow and trap moisture.
- Use the right tape. Always seal joints and connections with aluminium foil tape — not regular duct tape or gaffer tape. It holds better, seals properly, and lasts much longer.
- Don't squash it. A kinked or compressed flexible duct can dramatically reduce airflow. Give it enough length to route gently, and it'll perform far better.
Quality You Can Count On
Not all insulated flexible ducting is equal. Cheaper options often use thin insulation that loses its effectiveness quickly, foil jackets that tear during installation, and inner cores that flatten under their own weight. Our range uses quality materials that hold their shape, perform to their rated specifications, and comply with UK building regulations.
Whether you're buying one length for a bathroom fan or a full pallet for a commercial project, you can shop with confidence knowing you're getting ducting that does the job properly. If you’re n need any suggestions or have any questions, please feel free to reach out to us via emailsales@flexibleducting.com or call us on 0117 330 2277.
FAQs
1. What's the difference between insulated and standard flexible ducting?
Standard flexible ducting is just the inner pipe — no thermal jacket. It's fine for short internal runs where condensation isn't a concern, but for anything passing through cold spaces or longer runs, insulated flexible ducting is the better choice. The insulation layer prevents heat loss and prevents condensation from forming inside the pipe, protecting both your system and your building fabric.
2. Is insulated flexible ducting suitable for bathroom extractor fans?
Yes — and it's actually the recommended option for most bathroom installs. Warm, moist air from your bathroom travelling through a cold duct is a recipe for condensation. Insulated extractor fan ducting keeps the duct surface temperature stable, so moisture remains in vapour form all the way to the exit. No dripping, no mould, no blocked fans.
3. What size do I need for a standard bathroom fan?
Most domestic bathroom fans have a 100mm outlet, so 100mm insulated flexible duct is the most popular choice for home use. Check your fan's specification to confirm — it'll be listed as the spigot or outlet diameter.
4. How do I cut insulated flexible ducting to length?
It's easier than it looks. Pull back the outer jacket and insulation to expose the inner core, then cut the wire-reinforced core with tin snips or heavy-duty scissors. Trim the insulation and outer jacket to the same length, and seal the cut end neatly with aluminium foil tape before connecting your fitting. Done.
5. Can I use this ducting for a commercial kitchen or industrial space?
Absolutely. Our range includes sizes and specifications suited to commercial kitchens, industrial ventilation, and HVAC installations. If you're working on a larger project and need help selecting the right product or buying in volume, feel free to get in touch — we're happy to help.