soap flakes
US /ˈsoʊp ˌfleɪks/
UK /ˈsoʊp ˌfleɪks/

1.
small, thin pieces of soap, used for washing clothes or for making soap solutions
:
•
She added a handful of soap flakes to the warm water for delicate laundry.
•
My grandmother always used soap flakes for handwashing.