Vacuum flask cooking is an invention introduced to the Asian market in the mid 1990s. The vacuum cooker (燜燒鍋) is a stainless steel vacuum flask. The flasks come in various sizes ranging from 20-40 cm (8-16 in) in diameter, and 25 cm (10 in) tall. A removable pot, with handle and lid, is inside the vacuum flask. The typical user prepares a meal in the morning, heats the meal in the pot, places the pot in the vacuum cooker and returns home after work to enjoy a hot meal. Normally, reheating is not required as the food remains hot enough for consumption after 6 to 8 hours.