The jacket in a classic man’s suit always has a lining that helps to shape the jacket. These interlinings can be sewn or fused; fused lining is one that is glued to the wool in the suit.
This process meant that men’s suits can be manufactured at a lower cost while still giving shape to the jacket, and keeping the jacket in its original shape even after continuous use.
But there are some drawbacks to offset the price advantage. The unnatural stiffness of the jacket makes it appear rather stiff. The jacket can feel inflexible and unyielding, particularly in the chest area, and the inflexibility means the jacket cannot conform to the individual wearer.
Dry cleaning can produce bubbles in the lining when the wool is separated from the fusing; the glue can also degrade with time. There is nothing that can be done to remedy this. A suit jacket with a fused lining also becomes less durable and starts losing flexibility over time.