Water does not drop through an open umbrella of silk materials unless the inside of the umbrella is touched. This is due to
Answer Details
The phenomenon described in the question is due to surface tension.
Surface tension is a property of the surface of a liquid that causes it to behave as if it were a thin, elastic film. The molecules at the surface of a liquid experience a net inward force due to the cohesive forces between them, which causes the surface to contract and form a shape with the least surface area.
In the case of an open umbrella made of silk material, the surface tension of water prevents it from passing through the small gaps between the threads of the silk. However, when the inside of the umbrella is touched, the surface tension is broken at that point, allowing the water to flow through.
Capillarity is the tendency of a liquid to rise in a narrow tube due to the adhesive forces between the liquid and the tube. Osmotic pressure is the pressure that must be applied to a solution to prevent the inward flow of water across a semipermeable membrane. Viscosity is the resistance of a liquid to flow. None of these properties are relevant to the phenomenon described in the question.