Abstract: A swim fin assembly for increasing propulsion during swimming includes a sleeve that is worn around a lower leg while swimming. A plurality of fins is each hingedly coupled to the sleeve. Each of the fins is urged into a deployed position on a downstroke of the lower leg during swimming. In this way each of the fins frictionally engage water thereby increasing thrust generated on the downstroke. Each of the fins is urged into a stored position on an upstroke of the lower leg during swimming to resist frictionally engaging the water thereby reducing drag on the upstroke.