Is it possible to improve the airtightness of a ductwork after completion?

To improve the air tightness of existing air ducts, a method of sealing the ducts by applying a sealant using a spray atomizer was developed in the USA in the early 2000s and is now (since 2015) being used in Europe. This method [1] can reduce leakage in an installed air duct system by 66-86% and can therefore improve the air tightness after installation.  This can have other positive side effects, such as the impact on energy costs, indoor air quality & comfort or hygienic requirements.

References

[1] MEZ-AEROSEAL. https://www.mez-technik.de/en/mez-aeroseal.html