HIMARI 日葵 is the everyday model, with a symmetrical five-layer construction and an approximate thickness of 10 cm. SORA 宙 is the 12 cm flagship, with a balanced medium feel that is slightly softer and fuller. Choose by intended use, preferred feel and available space rather than thickness alone.
Use this answer as a buying guide before choosing between HIMARI and SORA: compare feel, thickness, storage, available size, and whether you want everyday Japanese bedding or a fuller flagship shikibuton.
Related: Series guide · HIMARI vs SORA ·