MLR is a project file associated with Mollier Sketcher, a software for modeling and simulating air dynamics in air handling units. The software is designed for advanced users. Mollier Sketcher was developed by Swedish company IV Produkt, established in 1969.

Mollier Sketcher is no longer broadly used, but version 2.1b is still available on developers website. IV Product Designer mostly replaces Mollier Sketcher in many applications and is the preferred solution.