Extreme climatic conditions are understood to be high temperatures and high air humidity and then causing high wood moisture content.

All currently produced Petrof grand pianos are tropicalized. That means all the wooden piano parts except the action are coated with varnishes that are resistant against infusion of air humidity. Outer polished surfaces are coated with polyester lacquers, other surfaces with polyurethanic or acrylic coatings. There are no open surfaces on the pianos that would enable absorption of air humidity. The Petrof Company steadily takes great care of instruments to insure humidity resistance, continually searching for more effective coatings to protect wood more efficiently.

Petrof upright pianos are produced in two variants. Standard instruments intended to climatic conditions of middle climatic zones have some edges or hidden surfaces without special finish. The instruments that are intended for extreme wet climatic conditions, the Tropics, are Tropicalized as well as all the grand pianos. That means all the surfaces including hidden surfaces are special coated with polyurethanic or acrylic coatings against diffusion of air humidity.