Well, this will get me in lots of trouble.
I like to use beads and I know they are very effective. But, that is separate from the discussion of PG above. Sorry Shilala, I believe your explanation is flawed.
If you put a solution of water and PG in a closed volume, it has a vapor pressure in the air above it that is controlled by the solution's concentration and temperature. See the graph here:
http://www.lyondellbasell.com/techlit/techlit/2518.pdf .
If you check, a 50/50 solution has a vapor pressure at 70F that happens to correspond to the vapor pressure of water in air at 70F and 70% RH. So, it will reach this equilibrium.
I used PG on florist foam successfully for many years and still do in aging 'dors. It works fine in different conditions. However, in recent years it has been stylish to hold cigars at less than 70% RH, which PG cannot do. The value of the beads is their ability to hold an RH of 60 or 65%, which they do well.