It depends on the doors and hinges, really, plus what is readily available for carcassing. Generally available sheet materials for carcassing will probably be the limiting factor with the choice being (lightest to heaviest) birch plywood (12 and 18mm - sometimes 15mm is available), hardwood ply (12, 15 and 18mm - can vary a lot in density) and MFC (15 and 18mm), although MDF and MFC weigh about the same. If you can get it poplar ply would be the lightest for a given thickness, but it tends to only be available in a few parts of the UK (e.g. where they build caravans, like East Yorkshire) followed by the so-called lightweight MDF (also called LDF), also a specialist product stocked for the furniture manufacturing trade
A traditional approach which is lighter would have been to choose a lightweight framing timber (e.g. poplar aka tulip wood), combined with thin panels (e.g. 6mm birch plywood). A way used in yhe past was to make up a softwood frame from 2 x 1in PSE and clad it with thin sheet material, but it takes a lot of effort to achieve an acceptable result
Mind if I ask what the end item is?