綿
めん · men · JLPT N3 · noun
cotton
🧶 綿 = 糸 thread + 白 white + 巾 cloth: white threaded cloth, cotton
The left side 糸 marks fibres and thread. The right side 帛 (白 white over 巾 cloth) is silk fabric, so the kanji means soft white fibre for cloth. Read alone as めん, as in 綿 cotton; as わた it means raw cotton wadding.
わた · wata · JLPT N3 · noun
cotton
🧶 綿 = 糸 thread + 白 white + 巾 cloth: white fibre spun into thread
The right side 帛 means white silk cloth, built from 白 white over 巾 cloth. Put the thread radical 糸 next to it and you get the soft white fibre that becomes cloth. For the sound, わた is close to water, and cotton soaks up water.