It has been proved from transmission line theory that the mechanism of microwave absorption in film is different from that in material. It is a simple result but has not yet been generally accepted by the research community. It is commonly argued that microwaves are trapped by the back-and-forth reflections in the film and then absorbed by material along the zigzag path and thus researchers believe the film need not be considered as a separate entity with its own unique properties. It is believed that the current theory for microwave absorption is supported by much experimental data. However, via such data, Part 1 demonstrates that the data can be interpreted differently and more accurately by invoking the crucial role of the film which will be further evaluated from a new perspective in Part 2 for the difference between film and material, and in Part 3 for multilayer film design.