Filter Material Treatment

Filter material treatment from Envirox enhances the ability of your filter media to resist a range of harmful environment stresses, including corrosion, abrasion, high heat, hydrolysis and viscous gasses.

We have a wide range of treatment options available as required by your dust filtration application. 

Fabrics are usually pre-treated to improve their mechanical and dimensional stability. The fabric can be treated with silicone to give better cake release properties. Natural fabrics (wool & cotton) are usually pre-shrunk to eliminate bag shrinkage during operation. Both synthetic and natural fabrics usually undergo processes such as singing, calendaring, heat setting and glasing.

Filter material treatment is characterised between felted media treatment and fibreglass media treatment.

Treatment for Felted Filter Media:


The surface of the needle felt fabric will have a slightly hairy appearance or so called fibre fuzz. In some applications this creates problems as dust can build up on the fibers which are very difficult to dislodge during the cleaning process.  The problem can be addressed by singeing the surface of the felt.  With swiftness the felt are moved through a gas flame which removes the high points of fibre fuzz. By singing the fabric the collection and formation of the dust cake, as well as its release during cleaning are improved.


Calendering is achieved by compressing the needle felt between two very large pair of heated rollers that physically squeeze the needle felt as it is passed through the gap between them.  This action melts loose surface fibres and the objective of this process is to modify the surface characteristics of the textile to vary how it responds to dust and flow. The smoother surface encourages the formation of dust cake while ensuring easy release.

Heat Setting

When fibers are manufactured they invariably have a tendency to shrink in length when heated substantially. After these raw materials are converted to filter felts, they need to be heat stabilized to ensure that any shrinkage in the final application is minimized.

There are a number of ways of achieving this, but in all it is required that the product is exposed to a temperature comfortably above the expected operating temperature. The material has then to be held at that temperature to ensure that the in-built stresses are relaxed out. During this process the fabric is stabilized which will exhibit minimal shrinkage at the anticipated operating temperature.

Oil and water repellent

Glazing is the high pressure pressing of the fibre at elevated temperatures.  The fibres are fused to the body of the filter medium.  Glazing improves the mechanical stability of the filter and helps reduce bag shrinkage that occurs from prolonged use.


A wide range of chemical treatments are available for the enhancement of felt properties, the major ones are as follows:

Oil and Water Repellent

The Oil and Water Repellent coating is used to prevent bags from blinding caused by accumulation of wet, sticky or agglomerating dust.  Our Oil and Water Repellent finish is applied by total immersion in a bath followed by drying and curing. This guarantees that every individual fiber in the felt is covered in a sheath of chemical which ensures very high and consistent levels of repellency.

A high performance chemical treatment which is designed to give an enhanced resistance to modest hydrolytic attack. Hydrolysis cannot be stopped in susceptible fibers, but this treatment will delay its effects.The treatment is available for application to almost the entire range of products and can frequently be used in conjunction with other product modifications

Acid Resistance

This coating is commonly used in applications with exposure to acidic environments and gases.  When used in these environments this coating can substantially extend the life of the filter media by stopping the acid degradation process.

Flame Retardant

Flame retardant chemistry enhances the flammability resistance of our felts to reduce the likelihood of sparks and flame in the gas stream.

 *Fire-resistant finishes are not flameproof, they are flame-retardant.

Microporous Foam Surface Coating

This enhancement works by reducing the size of the pores in the surface of the needle felt so reducing the likelihood of particle penetration.

The system can be applied to most of our felt products and helps keep dust on the surface.  This type of coating is also used in product collection applications and aids in the collection of the product being produced and helps maximize yields.

PTFE Membranes are used for the effective capture of particulate with high airflow capacity, while also enhancing the cake release action, improving filtration efficiency.This treatment system provides a durable coating of PTFE on the fibers which provides added chemical resistance in use. PTFE enhances filtration capabilities of fine dust particulates, while retaining high airflow and effective dust cake release.

Membrane Lamination

The process uses a state of the art laminating machine to bond an ePTFE membrane to the surface of a wide variety of substrates to provide a range of benefits such as reduced emissions, improved cake release and reduced pressure drop.

Treatment for Fibreglass Filter Media:

Triple Finish

Consist if a blend of silicone oils, graphite and Teflon, which combine to protect the glass fabric from abrasion, but only a limited protection for chemical attack. Recommended for used in cement production and metal foundry applications.

Chemical resistance

Uniquely formulated finish composed of a polymer to prevent chemical attack of the glass filaments and PTFE to provide superior abrasion resistance.  The finish is resistant to both acid and alkali attack. Recommended for any fabric filtration application.

Acid resistance

Consist of acid resistant polymers, PTFE, graphite and silicone oil. From a covalent bond with molecules on the surface of the glass to shield it from chemical attack.  Recommended for filtration of flue gasses to shield it from chemical attack.  Recommended for filtration of flue gases in industrial utility boilers and acid environments such as carbon black and fossil fuel.

Teflon® B

Teflon®B PTFE  particules encapsulated the glass fibres to prevent abrasion. Since PTFE does not bond to the glass filament, strong acid or alkaline environments could attach the fabric.  Recommended for use with utility base load boilers operating under mild pH conditions. 

Ensure your filter media is equipped to deal with the stresses of the dust of your industrial application!

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