In both the "Wookiee Hunt" Clone Wars episode and Revenge of the Sith, several Wookiees wear helmets.
Reference Images
Mohawk Helmet
Star Wars: The Complete Visual Dictionary
Page 180
Dressing a Galaxy: The Costumes of Star Wars
Star Wars Celebration III
Shoulder Pauldron
Star Wars: The Complete Visual Dictionary
Page 180
Dressing a Galaxy: The Costumes of Star Wars
Star Wars Celebration III
Plated Helmet
Dressing a Galaxy: The Costumes of Star Wars
"Star Wars Identities" exhibit
Star Wars: The Clone Wars: Season 3, Episode 22 "Wookiee Hunt"
War Shield
Star Wars: Episode III: Revenge of the Sith
Star Wars: The Complete Visual Dictionary
Pages 178 - 179
Dressing a Galaxy: The Costumes of Star Wars
Unknown Sources
General Information
Materials & Construction Techniques
Scratch/Hardware Build
Toy Conversions
Replicas