soft pants

Soft pants is an alternative term for sweat pants. It is especially apt for when the business of the day is concluded and you take off your hard pants to switch to soft pants. Soft and billowy, they are built for chilling and lounging. Often they are a hoodie-type fabric with an elasticized or drawstring waist-band.

"I'm just putting on my soft pants. What are you doing?"
Tawney | Rectify S01E04