Traditionally, acoustic panels made from 1" or 2" fiberglass or rockwool have been the acoustic treatment of choice in offices.
Fiberglass and rockwool panels are the most economical, and have the highest NRC value. The 1" panels have a typical NRC value of .80 to .85.
But, in the last few years, there has been a movement towards something more decorative: acoustic felt.
Acoustic felt 1/2" panels have an NRC value of .65 on the wall and .85 on the ceiling as acoustical baffles. To compensate for the lower NRC values, simply add more acoustic felt panels in your office space.