Abstract: Plainification' is regarded as a promising design methodology for metallic materials to decrease the degree of alloying and reduce the difficulty of recycling. In this paper, we introduced the idea of planification into composites and proposed the concept of plainified composites, in which multiscale structural design methods (i.e. interface engineering, defect engineering) were adopted to improve the properties and optimize the overall performance of composites. Without changing the composition of composites or increasing the filler volume fraction, the tunability of materials was fully explored and expanded by multiscale design methods. Based on a canonical composite system, the possibility, advantages and expected results of making composites plainified were demonstrated. The various design methods that could be applied to achieve plainified composites were also illustrated. The application of this design methodology was exemplified in carbon nanotube(CNT)/silicone elastomer(SE) composites through interface engineering towards a plainified composite absorber.