Hi, Duco is an NC lacquer. Nitrocellulose (also known as cellulose nitrate, flash paper, flash cotton, guncotton, and flash string) is a highly flammable compound formed by nitratingcellulose through exposure to nitric acid or another powerful nitrating agent.

Polyurethane coatings are considered polymers. They can be very hard and strong, providing exceptional wear resistance. They can also be more soft and ductile, so that the base material is allowed to stretch without destroying the coating. Polyurethane coatings are not flammable, so they can be used for some situations where combustion is occurring in the same environment. Care must be taken to limit the exposure of a polyurethane coating to ultraviolet light because it can cause the coating to degrade.

With green standards fast becoming the norm, PU is also available in water based variants that can be used to coat wood. They have a comparable performance to Solvent based PUs and are much easier to apply. They don't require elaborate spray equipment and also do not pose a health hazard as they can be brushed on.
PU polish is relatively safe polish with petroleum based solvents. The water based polish has fewer volatile organic compounds. While 2-part PU polish is free from volatile organic compounds.