Understanding filtration › 3. Filter media

CHAPTER 3.1

Fibres and what they can withstand

Before the weave, before the finish, there is the fibre. It sets the limits of the cloth: the temperature it tolerates, the chemicals that attack it, how well it holds up over time. The three most common fibres in liquid filtration have very different profiles.

Nicolas Ract · 7 min read · October 2026

Polypropylene (PP)

This is the most widely used fibre for filter press cloths. Resistance charts rate it good against common mineral acids (hydrochloric, sulphuric, nitric) and caustic soda, more mixed against ammonia and caustic potash, and not recommended with sodium hypochlorite (bleach) and certain aromatic solvents such as toluene [1].

Its main limitation is temperature: around 80 to 90 °C in continuous use [2], about 190 °F (88 °C) according to another chart [1].

Polyester (PES)

Polyester withstands considerably more heat: around 130 to 135 °C continuously [2], 275 °F (135 °C) according to another chart [1]. It resists many acids reasonably well, but is not recommended with alkalis (caustic soda, caustic potash, ammonia) [1] and has poor resistance to hydrolysis, that is, the prolonged action of hot water or steam [2].

Polyamide (PA, nylon)

Polyamide sits between the two in terms of temperature, around 100 to 110 °C continuously [2]. Its chemical profile is the reverse of polyester's: it tolerates alkalis, but is not recommended with strong mineral acids [1][2].

Comparison table

These indications are general: actual resistance depends on concentration, temperature and exposure time.

Summary compiled from charts [1] and [2]. Other, more technical fibres exist for severe conditions (high temperatures, aggressive chemistry); they will be covered in a supplement.

How to use it

• Start from actual conditions: maximum temperature of the product and of the washes, pH, cleaning agents, and not just the nominal composition of the slurry.
• Think about the washes: a fibre that withstands the product may not withstand the acid or alkali used to unblind it (see chapter 4.4).
• Check with a trial: an immersion test on a sample, followed by a trial on a few plates, remains the only reliable check.

Field experience: a cloth that has become stiff and brittle over its whole surface, with no localised tear, is often a sign that the fibre has been taken outside its temperature or chemical range (see chapter 4.1).