Mattress encasements can last anywhere around 10 years and even longer, depending on how well you care for it. Most of the products on our list specify that they're machine washable, but it's best to carefully read the cleaning instructions so that you're laundering it properly. Depending on how often you sleep on the bed, you should usually wash your mattress encasement every 2-3 months. If it's used on a guest bed, this can be done less frequently, or if you experience a bed bug infestation, washing more regularly is extremely important.