In an emergency a dressing may be improvised from a range of materials. To control bleeding a bulky pad may be made from a bundle of several facial tissues or from any clean, non-fluffy material. For a minor burn or scald, a piece of clean plastic kitchen wrap may be used initially. However, if the burn is serious, it is vital to use only sterile coverings to avoid the risk of infection. Cooling should be continued until a sterile dressing is available. Very light dressings are used on a minor wound to aid healing and most have a non-adherent surface. A non-adherent dressing is often covered on one or both sides with a plastic film containing many perforations. If only one side has a plastic film, that is the side to be placed against the wound. This allows fluids to pass through into an absorbent layer, to keep the wound dry.