Penny is considered a very beautiful woman. She has layered blond hair when we first see her in Season 1, Episode 1 ("Pilot"). She is of average height and has a nice hourglass figure. She is thin but obviously works out, as can be seen by her triceps.

She also frequently dyes her hair throughout the show. First, it's almost a bleach blond with some brown highlights, then transitions to a dirty blond with way more brown and stays that way for a while.