Thanks @Star - not easy to find house dresses in these warmer colours!
@Lisa I'm not sure actually - since it's secondhand, the label has rubbed off It's breathable like cotton, but you can see there's a bit of drape to the stiffness - so maybe a cotton viscose blend? Either way, it's perfect for my current WFH lifestyle!
That said, I agree with @Janet that it's not a very flattering look in public. I'm thinking of maybe belting it once I do (eventually) wear it outside. Maybe I could even throw on one of @Roxanna's 'demented grandma' jumpers & then 'rest' the welted hem on the belt buckle for a little structure? I usually just add a big blanket scarf if I get cold when I'm at home.