Material Talk - Episode 3: What is Polyester?
What is Polyester ?
Polyester was first synthesized in 1926 by W.H. Carothers in the UK. It is the most common fiber in the world derived from petroleum, polyester is polymerized and spun into filaments to create the fabric. There are a dizzying array of formulas of Polyester commercially available and used as fabrics, however all Polyesters display the common characteristics of: High breathability, excellent moisture wicking properties, and extremely low production costs.
Jeffery Jansen Sr. Engineer at the Madison Group found that polymers like Polyester and Nylon are inherently susceptible to molecular degradation through immersion in water through the process of Hydrolysis. Hydrolysis is the degradation of a polymeric material through contact with water, specifically the hydrogen cations (H+) or hydroxyl anions (OH-). For those of us non-engineers this means that getting Polyester paddling gear wet makes it fall apart which is somewhat ironic given that it is a staple of splash and water protection throughout the outdoor industry.
Polyester generally has a low tensile strength thus making it less suitable for fabrics in high wear areas of the body and will generally suffer in performance of longevity compared to a material like Nylon.
Absorption and Drying Speed of Polyester Fabric
Polyester fabric is a hydrophobic material generally absorbing only 0.4% of it’s weight in water. Due to the chemical properties of polyester, which does not readily absorb water, it has the effect of passing water to adjacent fibers. This effect which we often describe as “wicking” means that the surface tension of water causes it so spread out across the garment.
The water saturating the garment will spread both laterally, and through the garment. Thus sweat will move from the inner side of the garment to the outermost layer. This in turn causes the water to cover more surface area and evaporate more quickly. In our tests utilizing a flat garment and 50 mL of water we fount the following diameters of radial expansion after pouring the 50 mL of water on a test piece:
Cotton: 4 inches
Nylon: 6.25 inches
Polyester: 8.5 inches
This process is the main function that aids in the drying speed of a Polyester garment under dry circumstances. However a significantly lower moisture absorption rate also helps aid the drying speed since less total water is saturating the garment.
Heat Retention of Polyester Products
Polyester is also an extremely common insulation fabric. The fabric has excellent heat retention properties and is used as a synthetic insulation in sleeping bags, puffy jackets, and is often spun into fleece. We will be covering fleece in a separate article, however the hydrophobic nature of the material causes small air bubbles to readily form across the surface of the garment allowing it to retain heat well even when wet. For this reason, synthetic sleeping bags with polyester fill are generally recommended for camping in wet or moist conditions since polyester sleeping bags will retain heat more readily and for longer when wet
Polyester’s Environmental Concerns
A Cornell University study on biodegradation of various garments revealed that in composting tests, the cotton fabric samples suffered a weight loss of approximately 50-77% after 90 days. Under the same conditions, polyester showed only a 20% degradation rate.
Polyester can be recycled, however given the readily available supply of polyester and the relatively cheap manufacturing conditions companies are unlikely to recycle it due to the high cost of recycling the fabrics.
Some companies like Immersion Research are doing work to change this culture building their polyester suits like the 7-Figure Suit out of recycled water bottles.
Use of Polyester in Garments
Most Polyester garments tend to be base layers due to the high heat retention and propensity to shed water These properties of polyester tend to make outer shell layers feel warmer since continuous splashes tend to not aid convective heat loss in paddling environments.
Paddling outer layers also utilize ePTFE in their construction thus creating an interaction between the inherent properties of Polyester and the ePTFE layers. If you haven’t checked out our ePTFE article you can learn more about internal delamination of ePTFE, but one of the leading causes of drysuit failure is actually the suit being wet for long periods of time due to degradation in PTFE sandwiched between the layers.
Studies have shown that PTFE will degrade in the presence of water and metals like (gold, copper, zinc, silver, and iron) so equipment that integrates PTFE should be dried thoroughly to avoid degradation.
