About A Chair AAC 51 office chair by Hee Welling

Same five-star base, same gas lift, same dimensions as the AAC 50, but the shell is fully upholstered here. HAY describes it in the same terms: "a versatile and multifunctional office chair."

The upholstered shell, and what the textiles are

The shell is the same as on the naked shell models—molded recycled polypropylene, according to the HAY product sheet—but it is fully upholstered here. Foam is applied to the shell and then covered with the chosen upholstery: the feel is softer and noise is better dampened in high-traffic rooms. In return, upholstery must be cleaned by blotting rather than spraying.

The upholstery options offered here: Steelcut, a Kvadrat wool fabric with a dense, slightly granular surface (90% wool, 10% nylon); Hallingdal 65, a Kvadrat wool fabric (70% wool, 30% viscose), the house classic, which is highly durable.

The base: five-star, casters, and gas lift

The base is a cast aluminum five-star star base: HAY writes cast aluminum five-legged castor base, mounted on casters. Five stars rather than four: this is the standard for stability for rolling chairs, as a four-star chair tips over too easily when leaning forward.

A gas lift adjusts the seat height. It is a pneumatic cylinder: a pressurized nitrogen cartridge, activated by the lever under the seat, which lifts the chair effortlessly and locks it at the desired height. It is maintenance-free and can be replaced as a spare part if it eventually loses pressure.

Note on height dimensions. HAY publishes a single overall height for these chairs. Since the seat is adjustable by gas lift, this value corresponds to a given position, not a fixed height.