Closely contact it with heating plate of electric fumigation insect killer and volatilize/evaporate effective ingredient when electric power is applied. You can usually have insect killing effect of 13.2�� ~ 19.8��(4 ~ 6 pyeong) by using one sheet. Effective period of one sheet is about 13 hours and blue colored sheep is discolored and changed to white color about 13 hours after using it. At this time, please change it with new one.