Why do nail polish top coats get stringy when applied?

Question: Why do nail polish top coats get stringy when applied?

Answer: It’s all about the solvents in the top coat. Nail polish top coats are blends of several solvents, not just one type. They often are 20-30% or more of the formula. Some solvents evaporate quickly and can escape from open top coat containers, leaving the slower evaporating solvents behind. This causes a slow shift in the ratio of these solvents, which alters the top coat away from its original composition. Not only that, the total concentration of solvents is slowly getting lower. That means that all other ingredients become more concentrated. This leads to even further changes in the composition.

The polymers used in nail polish top coats are chosen because they can harden into smooth films within a relatively short time. Before the film hardens, it goes through a stage where it isn’t a flowing liquid, but it isn’t yet a hard solid. This “in-between stringy phase” is what you get just before the film hardens. If this is happening in the bottle, it’s likely because excessive amounts of solvents have escaped from the container, and the top coat is beginning to slowly harden in the container.

Keep the caps tightly sealed and containers tightly closed with the necks clean to prevent premature evaporation of solvents.