Thermal Polyurathane (TPU) is a soft flexible rubber like filament. It has great moisture resistance and high layer bonding strength and is suitable for your flexible projects. It also has a shore rating of 85A.
As with most softer filaments print speed will need to be reduced. A good starting point is around 40mm/s, but this could vary depending on the machine. You will also need a feeder system that doesn’t allow the filament to buckle and get caught around the extruder gear.