Many people flip their mattresses regularly in order to prevent uneven wear and tear. These people may find it getting harder and harder to do it each time, because it may feel like their mattress is getting heavier and heavier each time. This is not their imagination playing tricks on them, because in fact their mattresses are getting heavier with every passing day. Most mattresses are made of materials like cotton, a material that attracts oil from skin, moisture, dust mites and dead skin cells. All these extra materials get stuck in the cotton fibers of the mattress. Since there is no way to wash a mattress on a regular basis, these simply collect over time. Some mattresses have been recorded to have doubled in weight over a period of 8 to 15 years. This also means that as mattresses get older, they become a more place attractive for bacteria to grow and for dust mites and bed bugs to thrive.