Air distribution


Fabric Ducting has many different names, from Air socks (or airsox) to textile diffusers, textile ducts, canvas ducts (they definitely are NOT made of canvas!), from textile ducting to air sleeves or even wind socks.   We think Fabric Ducting & Diffusers is the most accurate term.

Prihoda products are usually acting as both supply air ducting (air transfer) as well as air distribution/diffusion into the occupied zone. We supply both types of system, (1) positive pressure distribution systems (supply air) and (2) negative pressure (extract /return air) ducting for exhausting air from rooms.


1/ Air outlet from a diffuser

Supply air (see V below) flowing into the diffuser through either end or an inlet spigot, can exit the diffuser in any of the following methods:

A – through an outlet end – air leads to another system/area

B – through microperforations – either 200  – 400 µm laser cut holes in the fabric

C – through perforations – laser cut holes with a diameter greater than 4 mm

D – through small fabric nozzles

E – through big fabric nozzles

F – through an adapter/outlet spigot – air is diverted to another system/area

G – through an outlet end – air leads to another system/area

Fabric ducting - Air diffuser


It always holds true that:  V = A + B + C + D + E + F + G (certain values of A, B, C, D, E, F, G may be zero)


2/ Air entry into negative pressure (extract) ducting

Perforations are used to allow extract air into negative pressure ducting.

Fabric ducting - Air duct


3/ Air transfer ducting

Ducting made from impermeable fabric or insulated ducting transports air to the destination WITHOUT diffusion. We have the technical ability to design and manufacture, branches, bends and other fittings for any situation.

Fabric ducting - Air transfer duct

Supply air is delivered through fabric diffusers using almost any diameter of laser cut perforation in any position on the duct circumference. This combination of any size and position of perforations provides an almost infinite number of design variations. The range of possibilities begins with low velocity diffusion and continues up to long-distance targeted air supply. Small perforations with a diameter of 200 – 400 µm, which we refer to as microperforations, are designed mainly for use as low velocity air diffusion. We use a series of 4mm diameter or larger holes, which we call perforations, to provide directed air supply. When calculating the air travel distance, the supply air to room temperature difference must be considered.

Fabric Diffusers are a universal air distribution tool and cover the entire range of air delivery patterns. We achieve the requested air distribution by selecting the correct air outlet method. We can combine the air outlet methods on a single diffuser duct in any pattern or ratio we wish.


Airflow Travel Distance from Fabric Diffusers

Fabric ducting - Flexible duct airflow reaches

Travel distance varies depending upon available static pressure and temperature difference.

Here you can see video of smoke tests

The air velocity at various distances from the diffuser can be calculated by our ’in house‘ design software which is being constantly refined and takes into account all associated design influences. These include specifically, positive pressure in the diffuser, position and dimensions of outlet openings, and temperature difference. In cases where the air velocity cannot be reliably calculated by the software (due to complex interaction of multiple air flows for example) we can provide these calculations by means of our Fluent software.


Airflow patterns created by PRIHODA design software

Fabric ducting - Ductwork Prihoda design software

Airflow patterns created by Fluent software

Fabric ducting - Air duct fluent

In general, Prihoda Fabric Diffusers operate at similar air flow velocities to traditional ducting. The maximum speed within the duct is dictated by aerodynamic noise in relation to the place of use. A further velocity limitation may be needed due to flow turbulence, which can cause vibration of the fabric. Specific conditions of flow, static pressure and weight of the fabric used must be taken into account.