Partition Specialties, PSI. Since 1958, PSI is the leading commercial interior specialty contractor in California and Northern Nevada. Offering tailored architectural wall products and more. Our team and services are considered a valued resource and respected business partner by others in our industry. Exclusive West Distributor of: SkyFold Vertical Operable Walls, Modernfold Walls and Klein Door Systems. Offering: Tate Floors and other products; allowing for flexible space planning.