PG vs PEG

[SeanGAR]

The reason propylene glycol reduces humidity is because the water vapor pressure (that controls humidity) is related to the mole fraction of water in a liquid mixture.

So you COULD use a low molecular weight PEG to control humidity, as long as it was soluble in water. Since you are changing the partial vapor pressure of water by decreasing its mole fraction, a large molecular weight compound such as PEG 3350 would be much less effective than propylene glycol (you'd need more PEG 3350 in a water mix than propylene glycol).

http://en.wikipedia.org/wiki/Vapor_pressure

You could even use ethanol to control humidity, but you'd be facing problems because ethanol is volatile. Propylene glycol has low volatility and thus useful in decreasing water vapor pressure and humidity when mixed with water.