General Specs: Multifilament Polyester Types Compared

Polyester is a category of polymers, and all polyesters share certain characteristics however there are some significant differences in physical properties among all the types of multifilament polyester.  Not all polyesters are the same.

Multifilament polyester yarns are made up of more than one filament or single thread-like object. Fil count tells us how many single filaments there are in a cross-section view of a single strand of yarn, which comprises the total denier. 

A denier measurement (den) is the weight in grams of a multifilament yarn that is 9,000 meters in length. Lower numbers represent finer sizes of filament yarn (or cut fiber), and higher numbers represent coarser sizes of filament yarn (or cut fiber). A common denier range, or the thickness of threads, for industrial multifilament polyester yarns is 110-6,000.

Many types of industrial multifilament polyester yarns are available from various manufacturers worldwide.

Depending on end use, the yarns are classified into types based on their inherent properties, including:

• High tenacity (HT)
• High tenacity low elongation (HTLE)
• Super high tenacity (SHT)
• Super high tenacity low elongation (SHTLE)
• Mid shrink (MS)
• Low shrink (LS)
• Super low shrink (SLS)
• High modulus low shrink (HMLS)
• High shrink (HS)

Different industrial markets use multifilament polyester yarns in different ways. Here’s a short breakdown of markets and the type of polyester yarns they require.

High Tenacity Yarn

• Seat belt
• Industrial sewing threads
• Industrial webbing, flat and round slings and tie downs
• Ropes
• Stator lacing
• Thermoplastic hose reinforcement
• Fiber-optic cable binders and ripcords

Super High Tenacity Yarn

• Thermoplastic hose reinforcement

Super High Tenacity Low Elongation Yarn

• Thermoplastic hose reinforcement

High Modulus Low Shrink Yarn

• Geo-textiles
• Tire cord
• Mechanical Rubber Goods (MRG) hose reinforcement

High Shrink Yarn

• Stator lacing

Low Shrink Yarn

• Coating and laminating
• Stator lacing
• Fiber-optic cable binders and ripcords

Super Low Shrink Yarn

• Stator lacing
• Fiber-optic cable binders and ripcords

Yarn Tenacity (cN/Tex or g/den)

Standard tenacity for multifilament polyester yarns is measured in grams/denier, which is force divided by linear density. For most industrial uses, the high tenacity (HT) classification is generally preferred.

For a yarn to have high tenacity, the industry-standard measurement is ≥ 7.5 g/denier. However, many manufacturers will not accept anything less than 9.0 g/den due to ultimate strength requirements. High strength from finer yarns offers higher yield with optimum tensile performance.

As manufacturers demand higher performance from their end product yarns, the need for a super high tenacity (SHT) yarn classification has become more and more apparent. A good example of this is automotive hose performance, where consistently high burst strengths are required above a comfortable safety factor. SHT yarns are expected to have a tenacity of ≥ 9.40 g/den with a consistent measurement of 9.80 g/den.

Continuous Multifilament Polyester Tenacity

The table below lists the different classifications of tenacity and the fiber types associated with each.

Yarn Shrinkage (%)

There are several methods for establishing the shrinkage of a yarn. The most common method is hot air shrinkage (HAS). Yarn HAS can be determined and listed through:

• The use of a ventilated drying oven and stand (this method is described in the American Society for Testing and Materials standard ASTM D204-02).
• The use of a thermal shrinkage oven such as a Testrite thermal shrinkage oven.

The shrinkage oven method is described in the American Society for Testing and Materials standard ASTM 4974-99 and is the most common method, described as a temperature-duration-weighting system of shrinkage measurement Learn more about shrinkage testing.

An example of the importance of hot air shrinkage in yarn specification is in hose manufacturing, a yarn is braided around the hose and then put through a vulcanization process. If the yarn does not have correct shrinkage values, it can drastically affect the integrity and appearance of the hose after the vulcanization process.

Continuous Multifilament Polyester Shrinkage

The table below lists the different groups of shrinkage and the fiber types associated with each.

Service Thread is a global leader in developing and manufacturing engineered yarns and threads. We help customers who are having processing and design challenges, or material availability issues solve these problems by sharing our diverse experience, global supply chain partnerships and advanced material processing techniques.

Our technical team is always available to help you choose the best industrial yarn for your application. Contact us for assistance today!