<p>As the cellulose raw material is mainly plant derived, the industrial applications of cellulose are expected to offer a natural circular eco system. One of the attractive target applications is in thermal management which is relevant due to the increase in the demand for data processing driven by online services and artificial intelligence (AI). Although the thermal features of cellulose nanofibril (CNF) have been energetically studied, the industrial applications leave room for further exploration. Inspired by natural plant leaves, a novel soft heat spreader device has been prototyped. The device design features multi-leaf shapes which consist of CNF films laminated on the substrate of a copper slit plate using CNF glue. The key concept of the device is the combination of the CNF films taking the role of heat exchanger with the surrounding air and the substrate helping the thermal conduction as well as retaining the device shape and integrity. The dependence of the thermal resistance on the device design variants was evaluated by measuring heater power required to maintain preset temperatures of the heater. Among the design variants, the cooling ability of a 6-leaf soft heat spreader was examined on a system on chip (SoC) board with a natural convection arrangement. The 6-leaf heat spreader showed a 2.9 °C cooling effect compared to 1.9 °C for the substrate only device. An empirical model inspired by natural leaf transpiration phenomena is suggested to explain the cooling effect.</p>