From Nevergrind Wiki

Any class can wear any type of armor, but certain classes will incur haste penalties if they equip armor that is too heavy for their class. Different armor slots also incur a higher penalty than others. For example head and chest items have higher penalties than waist or hand items. Haste penalties are applied to your global cooldown speed, or skill haste, and your casting haste. See the tables below for a complete haste penalty breakdown. Some items have a Reduced Weight property which drops their actual weight down one tier. This would allow a Wizards to wear leather armor without an armor penalty.

Plate Class Penalties

Warriors, Paladins, Shadow Knights, Clerics, and Bards may wear all armor types without an armor penalty.

Chain Class Penalties

Rangers, Rogues, and Shamans may wear up to chain without an armor penalty.

Armor Type Head, Chest Shoulders, Legs Bracers, Gloves, Belt, Boots Plate 5% 3% 2%

Leather Class Penalties

Monks and Druids may wear up to leather without an armor penalty.

Armor Type Head, Chest Shoulders, Legs Bracers, Gloves, Belt, Boots Chain 5% 3% 2% Plate 11% 7% 5%

Cloth Class Penalties

Necromancers, Enchanters, Magicians, and Wizards may wear only cloth without an armor penalty.