Why do they put polyester lining in woolen jackets and coats?
Compared to the other three popular lining materials, polyester is the least expensive, strongest and most durable. Some polyester is treated for extra-soft and anti-static properties to improve comfort. It’s also resistant to stain, wind, water, stretching, and shrinking, used for insulation. As textile technology advances polyester fabrics are gradually losing their bad reputation.
The Linings Feel and Texture
They do this so you don’t feel the wool next to your skin, which is itchy for a lot of people.
Even wool scarves and socks are itchy unless the weather is freezing. If it’s cold enough outdoors, the wool doesn’t feel as bad as it might feel in a warmer environment.
The reason for using polyester rather than say, silk is easy enough to understand.
#1 - People aren’t typically looking at the lining of someone’s coat.
#2 - Today’s polyester is typically a better quality than it was in the past.
#3 - The use of polyester keeps the costs down. If silk was used as a liner instead, the cost of the wool coat would skyrocket.
Lining interaction with the skin
The poly jacket lining makes it easier to slip your arms in and out of the sleeves where otherwise the unlined wool sleeves would interact with your shirt sleeves and bind and your arms would not slide in easily.
Additionally the lining prevents skin contact with the wool which can cause roughness and itchiness, which nobody wants.
There is nothing inherently wrong with polyester lining. Some expensive coats and suits use cupro (Bemberg) which is rayon. Manmade like polyester.
As others have said, wool needs to be lined, not just to make it more comfortable, but to help it hold its shape. A polyester is a good choice for a lining: it slides on easier than most cottons, doesn’t stretch, and is reasonably priced. It also won’t shrink with cleaning. It will also last as long as the wool, better than silk will. I have seen many vintage and older pieces where the silk lining was in tatters.