Overlay cushion with removable contouring members

A seat comprising a backrest comprising a contoured surface formed from a plurality of stackable contouring units that form raised areas and/or recessed areas, wherein the seat further comprises a flexible, customisable backrest overlay that substantially conforms around the contoured surface of the backrest, and that comprises a first layer having a front surface and a rear surface, wherein a plurality of channels are provided on the rear surface and extend in a first direction along the rear surface to allow the overlay to flex around the contoured surface of the backrest, wherein one or more first contouring members are located between adjacent channels and project from the rear surface of the first layer and wherein one or more second contouring members are located between adjacent channels and are attached to the one or more first contouring members so that the first and second contouring members form stacks of contouring members between adjacent channels, and wherein perforation lines are provided between the stacked contouring members to allow each second contouring member to be detached from the first contouring member in the same stack to adjust the contours of the front surface to provide customized contoured cushioning to satisfy the postural alignment needs of the user.