What is fluted filter paper?

Fluted filter paper is a circular piece of filter paper folded in an accordion style and used to filter solid impurities from a liquid during gravity filtration. The fluting of the paper increases the surface area of the filter.

Filter paper is fluted by folding a circular piece in half three times without unfolding the paper between folds. The paper is unfolded twice, creating a semicircle with four quarter sections created by the creases. Each quarter is folded in half using a fan fold by alternating folding up and down. The paper is unfolded back to a full circle and placed in a funnel. The liquid being filtered is poured through the filter paper and caught in a container below the funnel.