Alternating-pressure air mattresses (APAMs) have a long history, and after some advances in their design, which began in the 1980s, have become widely used for pressure sore prevention. A recent variation in the inflation/deflation cycle of a 'large-cell' APAM, which allows the use of lower (peak) pressures for inflating the air cells, is used in the Quattro range of APAMs. This should make the new products more comfortable, more versatile, and more durable than earlier large-cell APAMs. This article discusses both the theoretical and practical advantages and disadvantages of these products. It also suggests a simple method of checking the suitability of a given support for promoting a healthy skin for highly dependent patients.