Porous materials occur throughout nature and industry, from volcanic rocks, to sponges, through to filters; they comprise a solid structure, which could be like honeycomb or a packing of grains, with gaps (pores) throughout. These pores allows fluid and small contaminants carried by the fluid, such as salt in seawater, to travel through the material. The shape and size of these pores affects the passage of fluid, which in turn affects the path the contaminants take and how much becomes trapped within the solid structure.

Next time you lose your paddle whilst canoeing - don't despair. There is another way to push your canoe forwards: by jumping on it! Gunwale bobbing refers to the act of standing on the gunwales (side walls) of a canoe and forcing it into oscillations with one's legs. When forced at the right frequency, the canoe can surf from crest to crest of the generated wave field by pushing into positive surface gradients.