1. When washing woolen sweaters in a washing machine, they tend to shrink due to the structure of the wool fibers and the physical actions that occur during machine washing.2. The surface of wool fibers has a scale-like structure, which causes the fibers to tangle with each other during machine washing, leading to felting and shrinking.3. The vigorous agitation and friction inside the washing machine exacerbate the felting and deformation of the wool fibers, resulting in a reduction in size of the sweater.4. Wool fibers are prone to expansion and tangling when wet, and the actions of the washing machine amplify this effect, causing the scales to interlock and form a felt-like structure.5. The type of detergent used and the temperature of the water also affect the degree of shrinking. Using a mild detergent and cold water (no hotter than 30°C) can help minimize shrinking.6. Strong detergents or high-temperature water can cause more severe fiber felting, so to reduce shrinking, it is recommended to hand-wash woolen sweaters with a specialized detergent and control the water temperature.7. If a washing machine must be used, select the wool washing program and use a washing bag to reduce the impact of mechanical actions.