Avoid hanging them up as the fabric starts to stretch over time and lose its shape. For silk thermal underwear, hand-wash.

As a general rule (and the industry-standard), your underwear assortment should be refreshed every six months to a year. Or buy new underwear when it pleases you.

Cotton is a popular fabric for panties. However, when compared to silk, there are some essential differences that give silk a distinct advantage. Silk fabric is gentle on the skin and silk is a protein-based fiber and is naturally moisturizing. Silk is also naturally hypoallergenic, non-irritating, and resistant to mold and mites. Finally, silk panties have excellent breathability.

When the weather is cold, finding a pair with silk is perfect for you. It will give you more time to spend outdoors without freezing when you wear silk-long underwear.  It's light enough to wear under anything, and it helps lock in your body heat to keep you warm but not overheated. You'll stay warm and comfortable, and you won't be messed up by shivering while wearing silk long underwear as you do so. 

The answer is yes, silk boxers are very breathable. As a natural fiber, silk allows your skin to breathe, which is especially important for intimates.