The temple garments are one of the most mocked aspects of the Mormon faith. It is not that the people who mock the temple garments misunderstand their purpose. The idea of protective underwear seems odd to people outside the faith.
The purpose behind the temple garments is no different than wearing a cross, it is a symbol of the wearer's faith. Members of the Church of Jesus Christ of Latter Day Saints first receive the temple garments when going through the temple.
Many adult members wear the temple garments in place of other types of underwear. Mormon children do not wear these garments and will be dressed much the same way as children of other faiths are.
The temple garments are designed in a way to ensure standards of modest dress, but their chief purpose is to remind the wearer of the sacred covenants they promise to uphold during tne endowment rituals. According to the LDS Temples Website, which is not an official LDS church source, the garments help foster a state of obedience to the Lord, making it easier for a member to keep the vows that he or she has made in the temple.
The Temple garments are white in color for most members. Mormons who serve in the armed force are able to purchase garments in the colors prescribed by the perspective services, but the vast majority of temple garments are white. In the past, these pieces of underclothing had to be ordered from LDS sources and could only be ordered by temple recommend holders, but the two-piece underwear sets can now be ordered online.
Temple garments have two markings on the top half that conveys the power of the Holy Priesthood. While the garments are in good shape, they should be treated with respect, but after the garments become worn, the symbols should be cut off and then the temple garments can be used as rags or burned. The cloth itself is not holy without the symbols.
The reason that the temple garments, the holy underwear, get so much attention is that most people find the idea of sacred undergarments bizarre. Mormons do not talk about them and it is rather rude to ask to ask a Mormon friend or co-worker about the state of their underwear. The temple garments may seem bizarre to people outside the faith.
Sources:
LDS Church Temples – Article on Mormon Underwear
Washings, Annointings, and Other Rituals
Note: Although pictures of the temple garments can be found online, they will not be shown here because many Mormons consider them to be sacred.