Combi Flexible Fan Ducting has an aluminium and polyester inner shell, which is supported by a highly durable steel wire helix and given protection through an outer layer of PVC. This combination of parts provides a super strong yet remarkably flexible ventilation product, guaranteed to remain completely airtight and resistant against all grow room temperatures and pressures. For maximum effectiveness and to stop dust collecting in the ducting, always make sure your Combi Flexible Ducting is fully extended. It doesn't take much time or effort to install, weighs little and conveniently comes compacted and boxed up. Recommended!