The actress starred with the Golden Globe-winner in Legally Blonde and describes Witherspoon as a "sensitive little earthling".
Blair says, "Reese is the antithesis of Paris Hilton. She's never courted the tabloids or wanted to be on parade for the drama. She's about doing good work."
Witherspoon herself has lashed out at the endless supply of dumb-blonde types currently popular in Hollywood.
The WALK THE LINE star says, "It irritates me that the sort of fad that 'stupidity is cute' might really be doing some serious damage. It's the cheap answer, and let's hope that their moment fades. Sorry, but I have a little girl."