| CPC B65D 43/0208 (2013.01) [B65D 2543/00092 (2013.01); B65D 2543/00351 (2013.01); B65D 2543/00518 (2013.01); B65D 2543/00537 (2013.01); B65D 2543/00555 (2013.01); B65D 2543/00629 (2013.01); B65D 2543/00685 (2013.01)] | 11 Claims |

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1. A securely-engaging removable lid for a cup having a cup rim, comprising:
a central portion;
a secure engagement layer at the periphery of said central portion for secure engagement with said cup rim when said cup rim is seated in an interior concave contour of said secure engagement layer, and when unflexed an inside contour of said secure engagement layer having an overhang having cylindrical symmetry, said overhang protruding towards the axis of said cylindrical symmetry, and a dimensionless tightness-of-fit ratio Ψ being defined as
Ψ=δ E d3 C/4 m g L3
where m is a mass of liquid that can be contained in said cup, g is acceleration due to gravity of 980 cm/s2, E is a Young's modulus of the material of said securely engaging removable lid, C is a circumference of said secure engagement layer, δ is a depth of said overhang, d is a thickness of the material in said overhang layer, and L is a length from a top outside edge of said secure engagement layer to a central point of said overhang, the value of said dimensionless tightness-of-fit ratio Ψ being greater than 1400.
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