What are mormon temple garments/underwear?
Here is the answer according to the Official LDS site: Wearing the Temple Garment Once people are endowed, they have the blessing of wearing the temple garment throughout their lives. They are obligated to wear it according to the instructions given in the endowment. Those who have been endowed in the temple must remember that the blessings that are related to this sacred privilege depend on their worthiness and their faithfulness in keeping temple covenants. The garment provides a constant reminder of the covenants made in the temple. The garment should be treated with respect at all times. It should not be exposed to the view of those who do not understand its significance, and it should not be adjusted to accommodate different styles of clothing. When worn properly, the garment provides protection against temptation and evil. Wearing the garment is an outward expression of an inward commitment to follow the Savior.
