These are the reading trousers.
Their virtues are legion: they do not bite, itch, ride up, expose the ankles to drafts, generate electric shocks, or work themselves into vicious little wrinkles which dig in. They enable much intellectual endeavour (also sleep), and accommodate not only legs, but any size of lunch. Social graces should not be expected of the reading trousers when appearing outside the home, as they are not interested in public opinion. Indeed, at formal gatherings they may spontaneously fall down.
Every reader should have some.