Does the smoke from e-cigarettes leave an oily film on the glass window like the smoke from regular cigarettes?

Yes, the smoke from e-cigarettes also leaves a film on the glass window, but its composition, appearance and cleaning difficulty are quite different from the tar residue left by traditional cigarettes.
?? Different composition of residues
The films left by the two are chemically completely different:
Residues of electronic cigarettes: Propylene Glycol (PG) & Vegetable Glycerin (VG)
The "smoke" of electronic cigarettes is essentially an aerosol, with the core components being propylene glycol (PG) and vegetable glycerin (VG). PG leaves behind an oil-like film that is difficult to remove, while VG leaves behind a more viscous residue. This is direct evidence that the smoke from electronic cigarettes is not "water vapor".
Cigarette residue: Tar (TAR)
The smoke from traditional cigarettes leaves behind the well-known tar (TAR).
?? The appearance, accumulation and cleaning are quite different.
The fundamental differences between these two components result in their vastly different performances in daily life.
Comparison Dimension:
✅ Electronic cigarettes (PG/VG residue)
❌ Traditional cigarettes (tar residue)
Film Appearance:
Usually a transparent or light gray oily film.
Classic yellowish-brown stains, very noticeable.
Odor:
The odor is usually not strong and is related to the flavor of the e-liquid (such as fruits, mint), dissipating quickly.
The odor is persistent and intense, it is the well-known "smoky smell", which will deeply penetrate into fabrics and walls.
Accumulation Speed:
Relatively slow, but if frequently used in a confined small space (such as in a car), the accumulation is still considerable.
Relatively fast, which is why the rooms and cars of old smokers will quickly turn yellow.
Impact on Surfaces:
It will adsorb dust, making the glass look foggy and unclear.
Tar will directly penetrate and stain the surface, causing permanent damage.
Cleaning Difficulty:
Relatively simple, just use the cleaning agent several times or choose the appropriate tools.
Very difficult, requires strong cleaning agents and a lot of physical effort, and may not be able to completely remove it.
Effective Cleaning Solution:
Cleaning agents containing white vinegar (Vinegar) or isopropyl alcohol (Isopropyl Alcohol, with a content of over 70%) work very well. You can also use soapy water.
Requires specialized tar removal agents or extremely powerful cleaning agents.
?? Summary
In simple terms, electronic cigarettes do leave a film on the glass, but it is a transparent, mainly composed of propylene glycol and vegetable glycerin oily residue. Compared with the yellowish-brown tar residue left by traditional cigarettes, this oil film is easier to clean, has a weaker odor, and dissipates more quickly. However, to keep the view clear, regular cleaning is still necessary.