Fabric Properties: Wool, Cotton and Polyester
Introduction
Common fabrics such as wool, cotton, and polyester each have unique properties shaped by how the yarn/fibre is architectured (e.g., weave pattern, porosity and thread density).
Other physical characteristics are more familiar to consumers, e.g., grams per square metre (g/m²), better known as GSM.
Understanding these basic parameters helps consumers and designers make better-informed choices.
This article examines five functional characteristics: warmth, ultraviolet protection factor (UPF), moisture management, breathability, and sustainability.
It also considers the environmental impact of wool, cotton, and polyester through what is known as the life cycle assessment (LCA), quantifying the environmental trade-offs between natural and synthetic fibres.
By comparing these materials, the article provides a clear guide to selecting fabrics based on functionality and sustainability.
1. Warmth
Figure 1 shows the thermal resistance of wool, cotton and polyester during stationary conditions. <tt>2001</tt>
For context, the warmth of a fabric is often referred to, in textile science, as 'thermal resistance' (Rct) and reflects how well a material resists heat transfer (or heat loss) to the ambient air.
Researchers measure this thermal resistance of fabrics using a setup shown in figure 2, known as a guarded-hotplate test. <tt>2000</tt>
The test is principled as follows: a fabric with higher insulation properties (or thermal resistance) will lose less heat emitted from the hot plate it surrounds, so less electrical power is therefore required to maintain a constant plate temperature (e.g., 35°C), despite a lower (and fixed) ambient temperature (e.g., 20°C).
Despite very similar mass (grams/meter²), wool showed 105% higher thermal resistance than cotton and 69% higher thermal resistance than polyester.
Researchers largely attribute the enhanced thermal resistance of wool to its natural thickness, which is mostly made up of air pockets, trapped in the labyrinth of wool fibres.
These air pockets absorb and trap the natural warmth emitted from the human body.
Wool fibres also naturally have repulsive electrostatic properties which create fibres that crimp, rather than the linear and malleable behaviour seen in polyester fibres, which form a low-density, air-filled matrix that substantially contributes to thermal insulation.
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2. Ultraviolet Protection Factor (UPF)
Sunscreens and lotions are synonymous with ultraviolet (UV) protection. But the fabric of worn clothing can provide just as much, if not more, UV protection than sunscreen lotion alone.
A 2001 study published in BMC Dermatology involved transmitting UV radiation (across the 290–400 nm range) directly onto samples taken from a total of 236 tested fabrics, with the quantity of UV passing through each sample being measured. <tt>2002</tt>
Figure 3 shows the overwhelming majority of <u>wool and polyester fabrics achieved a UPF rating of 50+</u>, in stark contrast to cotton fabrics, in which <u>over 75% of samples achieved an UPF of under 30</u>.
Interestingly, due to the molecular properties, many of the wool and polyester samples achieved high UPF values. Wool fibres are made of keratin (~95% - 99%), a protein that contains aromatic amino acids (tryptophan, tyrosine, and phenylalanine) that absorb UV light, especially in the UVB and UVA range. <tt>2005</tt>
Similarly, polyester, being composed of a chain of terephthalate groups attached to ethylene groups, is believed to have a UV absorption effect, specifically due to the benzene ring within the terephthalate group. <tt>2006</tt>
However, not all wool and polyester samples blocked high doses of UV radiation in the study. This suggests other fabric parameters, such as fabric construction, including weave tightness and fabric thickness, also play a significant role. <tt>2007</tt>
A common metric used to quantify fibre density both in commercial retail of clothing and in textile science is grams per square metre (g/m²), marketed as GSM. This reflects the amount of fabric in one square metre of a given fabric.
A higher GSM often correlates with higher UPF protection but could also diminish breathability.
3.Moisture Management
Figure 4 shows the percentage of moisture vapour absorbed by wool, cotton and polyester fabrics at two humidity levels (45% and 85%). <tt>2001<tt>
In both humidity settings, wool demonstrates superior moisture regain (i.e., quantity of absorbed moisture vapour), cotton is intermediate, and polyester absorbs very little moisture.
The study determined these findings by calculating and measuring the energy released when water molecules form bonds with fibres of fabric, reflected by "transient heat peak area (kJ/m²)".
3.1 The Science in Context
During physical exertion, the skin-side microclimate experiences frequent spikes in humidity due to perspiration (sweating).
When activity slows, so does perspiration, and consequently humidity decreases.
Fabrics absorb moisture vapour and, in doing so, release heat from the chemical bonds as the fabric interacts with water molecules.
Conversely, heat energy is taken in during the opposite process, the drying (desorption) of fabric, as moisture vapour is released; this process stems from the breaking of chemical bonds between water molecules and the fibres of the fabric.
One shortcoming is the authors of this study did not quantify how well the fabric dries (desorbs) between wool, cotton and polyester, i.e., how well those fabrics dry during changes in humidity level.
Such results would have provided a more whole understanding of how a fabric would perform in managing moisture during extended periods of physical activity.
4. Breathability
The breathability of a fabric is often referred to as air permeability in textile science. And one of the parameters which determine air permeability is porosity, i.e., the quality of pores in the weave of the fabric architecture. <tt>2003</tt>
A recent 2025 study directly compared the air permeability of wool, cotton and polyester fabrics in each in the form of various fabric constructions (single jersey, terry knit, rib knit, mesh knit).
Polyester, being very malleable and linear, generally achieved higher air permeability than cotton and wool (besides the uncommon mesh-fabric construction), both of which tend to be thicker and crumple on themselves as they loop and, consequently, diminish the size of adjacent air channels.
Jumpers are a great example for explaining how fabric structures can affect an individual’s microclimate via fabric breathability and, consequently, suitability for various weather conditions.
Light crewneck and V-neck jumpers typically use a cotton fabric in conjunction with a <u>jersey knit construction</u>. This creates a lightweight and thinner fabric, used for mild weather or indoor settings.
In contrast, it is common for sweatshirts to use cotton fabric in conjunction with a <u>terry knit construction</u>, characterised and observed in this study by low air permeability.
Although likely a thick and heavier fabric, this construction is favourable since it has traditionally been used to give warmth in colder weather.
For activewear, a fabric construction with high air breathability is preferred, like <u>polyester</u>.
Figure 5 shows polyester single jersey was found to be 198.75% as air permeable as cotton single jersey fabric construction. This is one parameter which makes polytester preferred in sport activewear.
However, polyester often comes with poorer moisture management. Hence, a blended fabric material is increasingly sought by manufacturers and consumers.
It is also important to mention, as did the researchers, other parameters, such as thickness, loop length, porosity, and density, also contribute to the air permeability of fabrics.
5. Sustainability
One of the methods researchers use to assess the sustainability of a material is known as the life cycle assessment (LCA).
This assessment evaluates a product’s total environmental impact from “cradle to grave”, including extraction of raw materials, production, processing, consumer usage, and end of life (disposal or recycling).
A report published by The Swedish Foundation for Strategic Environmental Research (MISTRA) quantified the greenhouse gas emission (GHGE), measured in CO₂ equivalent (kg) per kg of fibre, for the life cycle of wool, cotton and polyester, shown in figure 7. <tt>2004</tt>
Wool happened to have the highest greenhouse gas emission (GHGE), with an average of 16.8 CO₂ equivalents (kg) per kg of fibre. Although 75% was attributed to the methane gas, which has a global warming potential (GWP) 28 times that of carbon dioxide (CO₂), released as a result of enteric fermentation in sheep.
The production of cotton produces much lower greenhouse gas emissions (GHGE) compared to wool. Although being a plant fibre, it requires 860% more water than wool and 4700% more water than polyester for production.
Surprisingly, the production of cotton and polyester, on average, involves comparable levels of greenhouse gas emission (GHGE).
However, greenhouse gas emissions (GHGE) do not include the ecological costs of the large volume of unrecycled polyester fibres that seep into and diminish the environment and habitats (e.g., marine life).
One striking finding for the report by MISTRA was how much greenhouse gas emission (GHGE) can be reduced by extending the lifespan of a single garment, known as the impact per wear.
If a consumer wears a cotton or polyester t-shirt 60 times instead of 30 times, they can halve the greenhouse gas emission (GHGE) by amortising the environmental load over many uses.
Conclusion
In conclusion, wool, cotton, and polyester each offer distinct strengths and limitations across key fabric properties.
Wool excels in warmth and moisture management, cotton provides comfort and moderate performance, while polyester stands out in breathability and durability.
However, no single material is superior in all aspects, and trade-offs are inevitable.
Sustainability further complicates these choices, as environmental impacts vary depending on production and usage.
Ultimately, selecting the right fabric depends on balancing performance needs with environmental considerations.
By understanding these factors, consumers and designers can make more informed, responsible decisions when choosing materials for different purposes and conditions.