Definition of Motion Separation

Meaning of the Term as it Pertains to Mattresses

What is Motion Separation?

A mattress's ability to reduce and limit the spread of vibrations, motion separation, also referred to as motion isolation, is a feature that benefits sleeping partners. One partner's movements, such as tossing and turning or getting out of bed, can send vibrations through a mattress. This vibrational force, also called motion transfer, is often enough to wake a partner out of restful sleep. Motion separation limits motion transfer and allows for a partner to sleep uninterrupted. Motion separation has classically been illustrated in advertising through visual examples like a bowling ball being dropped on a mattress with pins set up close by or a person jumping on the mattress next to a glass of wine.

Motion separation is quantifiable through the motion separation index (MSI). The linear scale begins at 0 and reaches 230. The higher the number, the less motion is detected, which means a mattress will have better motion separation. An average mattress measures between 40 and 60 MSI. Top quality mattresses usually measure from 170 to 200 MSI. Some manufactures, like Simmons, simplify the scale and list MSI between 1 and 3, with 1 representing low motion separation and 3 representing the best motion separation. Innerspring mattresses that use independent coils, memory foam, and latex foam offer some of the highest MSI numbers in the market.