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 0.2mm or 0.4 mm laser cut holes in the fabric

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

D - through fabric nozzles – see chapter 5 for more details

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

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


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


2/ Air entry into negative pressure (extract) ducting

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

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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.

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Airflow Travel Distance

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 0.2 or 0.4 mm, 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

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


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.


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Airflow patterns created by PRIHODA design software


Airflow patterns created by Fluent software


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.




As a company PRÍHODA s.r.o. places tremendous importance on the quality of the materials used. In every case we use specially developed materials that have been subjected to extensive development testing in order to achieve maximum performance benefits for our customers. The PMI/NMI fabrics provide all the benefits listed below as part of our standard design (at no additional cost).










List of most important benefits of our fabrics

High rigidity and strength

Our basic PMS/NMS/PMI/NMI fabrics demonstrate optimum rigidity of 1800 N/10mm in the texture and 1000 N/10mm in the weave. These parameters make tearing of the material in normal use almost impossible.










High fire resistence

The PMI/NMI fabrics are certified to European standard EN 13501-1 with excellent results. In this test our fabrics achieve B-s1,d0 classification, which means prevention of spread of fire, minimum smoke production and no burning drops. NHE fabrics in fact meet class A requirements. PMI/PLI fabrics are also certified to US norm UL 723.










Negligible fibre shedding

Due to the use of endless fibres, ALL of our fabrics can be used in cleanrooms up to ISO Class 4. Independent laboratory tests demonstratethat there is practically no particle shedding from our material during operation.










Antistatic effect

Woven carbon fibre in PMI/NMI materials removes any build up of electric charge from the surface of the fabric.










Antibacterial effect

We utilise a special treatment which guarantees that no bacteria can survive if settled on to our fabric. This treatment remains effective after multiple washing. Tests for the European standards found that after TEN washes there was no reduction in the efficacy of the treatment.  This allows us to offer a 10 year warranty on the basis of our minimal maintenance requirements (see the following point).










Easy to maintain

Our fabrics which are manufactured using endless fibres are very effective and do not allow settlement of impurities from the supply air. This supply air is distributed through the diffuser perforations, and the Fabric Ducts remain relatively clean inside (in a normal environment). They do not require any other maintenance than outer dusting. Washing is normally only required for either hygiene or aesthetic reasons.










Stable Appearance

Thanks to our endless fibre technology, the appearance of the fabric does not change over time, or with multiple washing cycles, unlike materials made of basic fibres. Our PMI/NMI/PMS/NMS materials remain aesthetic after many maintenance cycles.












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How to Choose a Suitable Fabric?

When selecting material, please bear the following in mind


1/ Fire Resistance

Our fabrics show 3 levels of fire resistance.

Peak fire resistance (specified using the letter“E”, as in „Excellent”) means an entirely non combustible material. Within this class, we only use fabrics constructed from fibreglass with a polyurethane coating. These are however non permeable and more fragile than polyester fabrics of medium weight.










Increased fire resistance (specified using the letter “I”, as in “Increased”) means practically non combustible and very low smoke production. These materials meet the requirements for use in majority of spaces.










Standard polyesters or foils (specified using the letter“S”, as „standard“ or “F”, as in “foil”) have a very low fire resistance. They can be used in an environment where no fire resistance is required.










2/ Rigidity and Cleaning Ability

Fabrics are divided into 3 categories by weight.

Light (marked “L” ). These fabrics have a mass between 70 and 120 g/m2. Diffusers made from these materials only require 20 Pa of static pressure to achieve good inflation. However, they are light weight and have lower rigidity and increased risk of tearing if used out of specification. All our lightweight materials can be machine washed with the exception of NLF.










Medium (marked “M” ). These fabrics have a mass between 180 and 350 g/m2. They display the highest rigidity and anti-tear resistance. The minimum static pressure required for good inflation is 40 Pa. All of our medium weight materials can be machine washed.










Heavy (marked “H” ). These are PVC or polyurethane-coated fabrics and are only available in a non permeable specification. They cannot be machine washed but can be hosed or sprayed down. This makes our heavy materials suitable for the most contaminated environments. The minimum static pressure for good inflation is 50 Pa.










for any Farther Information Please check Prihoda