From Humanscale:

World LM, the streamlined edition of the original World, offers the same groundbreaking tri-panel mesh backrest and weight-sensitive recline for effortless ergonomic support. With fewer parts and a focus on simplicity, and delivers exceptional comfort and performance without compromise—now with the added option of a sculpted foam seat upholstered in a select range of textiles.

• All-mesh or upholstered design fits beautifully into any environment.
• Inspired by clothing design, World LM’s tri-paneled Form Sensing Mesh back takes on the exact shape of the sitter’s back, as if it were made for them.
• Lightweight construction makes it exceptionally easy to assemble and relocate.
• World LM is backed by a 12 year warranty for parts and components, and a five year warranty for arm pads and textiles.