Leather, silk, cashmere, thick wool garments, and any natural fiber materials that could be damaged by compression should not be vacuum sealed. This may include woven items, hemp, or items with feathers. Basically, if a garment should not be compressed or squashed, it should not go into a vacuum-sealing bag. Leather can also be cracked over time from the compression of vacuum storage. However, if you have items made of these materials that will not be damaged by compression, vacuum sealing them is likely fine. Proceed with caution and use common sense. Also, read any clothing labels or tags.