The design of the procedural masks (often referred to as “surgical” masks) depends on the mode; usually, the masks are three-ply (three layers). This three-ply material is made up of a melt-blown polymer, most commonly polypropylene, placed between the non-woven fabric. The melt-blown material acts as the filter that stops microbes from entering or exiting the masks. The inner and outer layers are fluid resistant that stops airborne droplets from entering or exiting the user's nose and mouth. Pleats are commonly used to allow the user to expand the mask such that it covers the area from the nose to the chin. The masks are secured to the head with ear loops, head ties, or elastic straps. Typically, the normal time you can wear a mask without changing it is about 4-hours. As the melt-blown polymer becomes full, the user will have a more difficult time breathing and the user's face will become hot very quickly. Masks made of non-woven material cannot be washed, so they must be disposed of after use.