It’s the heat. Wash your wool at the lowest temperature (20°c or no heat) and it’ll be fine.
In this regard, hand wash makes no difference. If you hand wash it in warm water it’ll also shrink. The reason why hand wash is recommended is to avoid tearing of finer wool fabrics. Wet wool tears easily.
Machine drying will also shrink it, because of the heat and the risk of tearing is also a problem there. Better to hang dry.
If you have already shrunken your sweaters, you can use a steamer or iron with steam functions or a regular iron and a wet rag. When the wool is hot and damp, you can reshape it. Be careful not just to stretch it wildly in all directions, because that’ll likely just make it a funky shape. It’s usually lengthwise that needs the most stretching because it shrinks proportional to the individual pieces of fabric.
You should always stretch fine wool after washing before hang drying. Otherwise it will shrink.
Tl:dr; wash without heat, stretch it while hang drying.
It’s the heat. Wash your wool at the lowest temperature (20°c or no heat) and it’ll be fine.
In this regard, hand wash makes no difference. If you hand wash it in warm water it’ll also shrink. The reason why hand wash is recommended is to avoid tearing of finer wool fabrics. Wet wool tears easily.
Machine drying will also shrink it, because of the heat and the risk of tearing is also a problem there. Better to hang dry.
If you have already shrunken your sweaters, you can use a steamer or iron with steam functions or a regular iron and a wet rag. When the wool is hot and damp, you can reshape it. Be careful not just to stretch it wildly in all directions, because that’ll likely just make it a funky shape. It’s usually lengthwise that needs the most stretching because it shrinks proportional to the individual pieces of fabric.
You should always stretch fine wool after washing before hang drying. Otherwise it will shrink.
Tl:dr; wash without heat, stretch it while hang drying.