The sit-to-stand (STS) is a common activity of daily living (ADL) yet recognized as one of the most biomechanically demanding. Impaired STS motions can lead to greater injuries from falling, and knee extensor strength has been identified as the primary limiting factor. To overcome this deficiency, several exoskeletons exist that offer actuated knee joints, but their hard and bulky parts make them uncomfortable and unfeasible for daily usage. Thus, the objective of this research was to develop an unobtrusive knee assist wear that can aid in the STS by assisting knee extension using only soft and passive components. A biomechanical simulation and experiments on the reduction in joint loading, metabolic cost, and muscle activity were done to evaluate the effectiveness of the device in providing unobtrusive knee extension assistance to help the STS. Simulations demonstrated a reduction in joint loading, and metabolic cost significantly decreased when utilizing the designed device for STS. Muscle activity of the knee extensors decreased on average across subjects but failed to show statistical significance. The present work introduces a new soft knee assist wear that aids the STS and shows promising results for the future development of soft assistive devices in assisting other ADLs.