satin
繻 centers on a specific type of smooth, glossy fabric: satin. The meaning is narrow and concrete, referring to the textile itself.
繻 combines 糸 (thread/silk) with 需, which likely contributes the sound. The character was created to name a specific type of silk fabric.
The left side is thread 糸, and the right side 需 looks like rain 雨 over a beard-like shape 而. Imagine rain falling on fine silk threads, making them smooth and glossy like satin.
For シュ, picture a bolt of satin being used to make a shoe: shoe -> シュ, and the smooth fabric becomes a fancy shoe.