Defrosting trays work by conducting room-temperature air into the frozen food while forcing the colder temperatures from the frozen item into the board. This transfer raises the temperature of the food so that it will defrost faster.
Many defrosting trays are made of aluminum, which is a good conductor of heat. Most tray designs include legs that elevate the board to allow warm air to circulate around it.
One way to make the board defrost food faster is to run hot water over it before placing the food on top. The tray will hold the water's heat and speed up the thawing process.
A Baltimore Sun article reviewing the boards says they work best with smaller food items, such as chicken breasts and hamburger patties. However, the boards did not defrost food as quickly as their manufacturers claimed. One manufacturer said that product owners get the best results when the meat makes direct contact with the board. Defrosting tray makers say that results may vary, depending on the temperature of the room and the thickness and density of the frozen food item.
Fans of the trays like that the defrosting meat stays cold and dry; it doesn't create messy liquid.