Mechanical Engineering: The hyperelastic physics behind EcoFlow's IP68 waterproof cable connections

When routing heavy-duty solar extensions or connecting Power Kits outside your rig, the cable junctions are exposed to torrential rain and deep puddles. EcoFlow uses aviation-style threaded connectors rated for IP68 (capable of continuous total immersion in water). The physics of keeping water out relies on the unique properties of elastomeric polymers.

Unlike metals, the rubber O-rings inside these connectors have a Poisson’s ratio of roughly 0.5, meaning they are hyperelastic and virtually incompressible. They behave exactly like a highly viscous fluid that maintains a solid shape.When you screw the threaded collar together, you apply an axial mechanical load. Because the O-ring cannot compress its volume, the rubber undergoes radial deformation—it physically bulges outward, pressing fiercely against the inner walls of the gland.

But here is where fluid physics (Pascal's Principle) takes over: if hydrostatic water pressure from a puddle tries to force its way into the connector, that external water pressure physically pushes against the rubber ring. Because the elastomer transfers pressure equally in all directions, the incoming water pressure actually forces the rubber to seal tighter against the opposite metal wall! Up to the material's extrusion limit, the deeper the water, the stronger the seal becomes.