Abstract: The invention relates to a seat insert (10), in particular for a motor vehicle or an aeroplane seat (30). Said insert is provided with a gas-tight covering (11). The covering (11) at least partially encloses a volume (14) and has an inner surface (12) and an outer surface (13). Also, the seat insert (10) is provided with a valve (40) which can regulate the amount of gas in the volume (14). The covering (11) comprises at least one climatisation section (15a, 15b, 15c) which is provided with a perforation (16). The aim of the invention is to produce a seat insert which very comfortable to sit or lie on and which is comparatively simple and economical to produce. The seat insert is provided with an upholstery element (20) which is made of an open-celled soft foamed material and is connected in a material-fit to the inner surface (12) of the covering (11).