Abstract: In a liquid storage tank having a floating roof with a circular rim, a substantially ring-like vertical cylindrical shoe adapted to slide along the inside wall surface of the tank outwardly from the roof rim, a primary flexible seal extending from the roof rim to the shoe, and with the shoe containing a plurality of vertically positioned spaced apart flexures in the form of an open ended trough which terminates below the shoe top edge and with a longitudinal opening substantially flat against the tank wall, the improvement comprising a flexure closure of resilient polymeric material with a lower body portion inside the open top end of a substantial number of the flexure troughs, with the lower body portion being in contact with the trough; and with the flexure closure having a thin flat upper portion placed by the shoe inside surface.