robe
褞 centers on a robe, a type of long, loose garment. The meaning is specific to this clothing item.
褞 combines the clothing radical 衤 with 昷, which likely contributes the sound. The exact historical development is uncertain, but the structure suggests a phono-semantic compound where 衤 indicates a garment and 昷 hints at the pronunciation.
The left side 衤 is the clothing radical, and the right side 昷 looks like a sun 日 over a dish 皿. Imagine a robe laid out flat, with the sun warming it like a dish set out to dry.
For ウン, picture a robe so comfortable that you let out a satisfied 'un' sound (like a relaxed grunt) when you put it on: 'un' -> ウン.