Why would polyester need drycleaning?

[Souper]

I bought a jumpsuit at Coast a few months ago and then proceeded to get breast milk all over it... It is 100% polyester according to the label but the care instructions say dry clean only! Surely it will be okay on a gentle cycle in the machine?

I'd risk it, probably wouldn't have checked washing instructions in the first place

DD works in the fabric industry and says that labels like that are due to clothing companies being too tight to pay for fabric testing so they just shove on the label that won't have people claiming their clothes have died coz they boiled washed them or something.

Probably won't apply to jumpsuit, but for jackets etc fabric is often backed by non washable interfacing eg on collars and lapels. The outer fabric washes fine, but the inner stuff does not, or does so differentially ...