BACKGROUND: Passenger comfort is a key variable in user acceptance of transportation systems. The back rest of a seat is of importance part in this experience. In designing a backrest, information of the human contour is useful as the product can be formed following this contour. The question is whether there is too much variation due to variety in tasks or in human anthropometry to design a back rest. OBJECTIVE: The research question is whether anthropometric properties and the performed activity have an influence on the back contour of a person. METHODS: The head, neck and back contour of a human sitting in an aircraft seat are estimated by using a kyphometer. In total 46 subjects are measured in two different chairs, when performing two different activities. RESULTS: This research indicates that the maximum variation of the contours occur on the upper back, neck and head. These parts are more bended forward when using a laptop compared with watching IFE. By dividing the data in groups, based on buttock-top of head distance, the height at which significant differences between the groups occur was determined. For one seat 400 mm above the seat pan a significant difference was found and for the other seat this was 420 mm above the seat pan. CONCLUSIONS: Differences in back contour started to appear above 400 mm vertical distance from the seat pan, which means that the design of a seat should facilitate this variation.