noun
fabric softener
A laundry product added during the rinse cycle to soften fabrics and reduce static cling.
洗濯の時に柔軟仕上げ剤を入れています。
I add fabric softener when doing laundry.
洗剤 is a general term for detergent or cleaning agent, while 柔軟仕上げ剤 specifically refers to fabric softener used after washing.
Compound of 柔軟 (じゅうなん, 'soft, flexible'), 仕上げ (しあげ, 'finishing'), and 剤 (ざい, 'agent, chemical'). Literally 'soft-finishing agent'.