Nature of the stains appearing on an upholstery fabric of a car's ceiling is the following: an extensive area of the ceiling; storing/keeping a car on the outside and/or in parking (temperature drop); waterproof fabric, which the covering of a ceiling is made of, is prone to accumulation of moisture, thus leading to water condensation between ceiling and its covering; exceeding the critical mass of the water accumulated leads to its dripping and following generation of blots at the edges of the covering. While aformentioned problems appear on clients' cars, proffesionals remove residual moisture through the inlet of an interior lamp.
Sorry that I've had to revise it so drastically, but it is now more understandable at least to me.
Cause and nature of extensive stains appearing on the upholstery fabric of a car's headliner:
When a vehicle is stored outside and/or in a parking area without temperature regulation, the waterproof headiner fabric is liable to accumulate moisture, leading to water condensation between the car roof and its covering. When the accumulation of water exceeds the capacity of the headliner to absorb and contain it, the water drips and generates blots at the edges of the covering. When this problem appears on clients' cars, professionals remove residual moisture through the base of the interior lamp fixture.
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