This thesis documents the development of a sustainable biomaterial made from unfiltered seaweed. Through a more-than-human lens it examines the complex reality of designing sustainably today, gathering insight in a series of “design lessons”. The development process cycles through harvesting, testing and reflection. A hands-on approach allows a relationship to form between human and seaweed. The end result is a biodegradable material made from unfiltered macroalgae. Through smell, texture and colour it clearly displays its origin, provoking a sensory and emotional response in the viewer. The gathered "design lessons" point towards what a sustainable increase in production of seaweed biomaterials might look like. The end result is both a practically useful plastic alternative, and a material to think with.