A method of making a bladder (100, 200, 300, fig 3-5) is disclosed in which a mask 6 is first placed at a weld location between first and second sheet portions 5, 8. The method includes welding a fluid connector 7 to the first sheet portion 5 at or adjacent the weld location such that the mask 6 prevents the second sheet portion 8 from being welded at the weld location to the first sheet portion 5 and/or to the fluid connector 7. The method also includes welding the first sheet portion 5 to the second sheet portion 7 to describe a sealed bladder (100, 200, 300). The welding of the sheet portions 5, 7 is concurrent with at least part of the welding of the fluid connector 7 to the first sheet portion 5. A first tool 2 may include a flat upper surface forming a substrate 21 for receiving a layered arrangement 4 including sheet portion 5, mask 6, fluid connector 7 and sheet portion 8. A second tool 3 may include a welding head 30 having a welding surface 31, which is a flat lower surface of the welding head 30 partially interrupted by cutaway portion 32.
