Yes, polyester material is windproof but when the polyester threads are woven together it creates the pores or gaps between the fibers and yarns which allow the air to pass through.
So in a sense, on its own, no polyester fabric clothing is windproof unless it has the support of technical fabrics like GoreTex Windstopper, Polartec, Dryline, etc.
But, it is known that getting windproof polyester fabric with better breathability is possible if we weave the microfilament yarns with high densities.
Let’s look at some technical details to get a better understanding of how windproof or wind-resistant the polyester fabric can be.
In scientific terms, the wind resistance of a polyester fabric can be measured by the air permeability of a given piece of fabric.
Air permeability is the rate of airflow per unit of fabric at a standard air pressure difference across the faces of the fabric.
Now, without complicating any further, the air permeability (wind resistance) of polyester fabric depends on the characteristics of the pores, like its dimensions, porosity, and distribution.
And for woven fabric, all the above things are directly affected by the number of yarns per unit area, fabric weight, fabric thickness, yarn linear density, and weave type.
So if you tweak these with a certain understanding of manufacturing textile then you can increase or decrease the wind resistance of given polyester clothing according to your wish.
The pores of fabric can be classified into three categories – pores between the fibers, between the yarns, and inside the yarn itself.
Mathematically, the dimensions of pores between the yarn are directly proportional to the yarn thickness and the yarn density.
So, if you increase the yarn density, the pores become smaller meaning there is an increment in wind resistance.
And, the dimensions of pores between the fibers and inside the yarn itself are depended upon the fiber fineness, yarn count, yarn twist, and crimp.
Flattening and deformation of yarn can also be taken into consideration.
In short, if you decrease the filament fineness the wind resistance of polyester clothing will increase because the air gaps between the filaments within the yarn become smaller which prevents the airflow.
Let’s get some depth…
According to research, as the filament fineness decreases, the number of filament increase in the yarn cross-section which results in the smaller void area between the filaments for finer filament, and the total surface area of the filament also increases.
Thus, as the interstices in polyester fabric increases in size and number the air permeability increases which means the clothing will be more breathable but less windproof.
Now, on the more scientific side, the higher weft sett values reduce the size of gaps between the yarns and thus lead to lower air permeability.
In conclusion, you should go with tightly woven fabric constructed with microfilament polyester yarn if you want the maximum amount of wind resistance.
Also, they will insulate you well against the wind.