only if your humidifier is not already charged with pg. Most are! But i have home made several. (1) travel soap container, a brick of green flower foam cut to fit, distilled water and PG.

Propylene glycol is a humectant - Sucks up water.

So if you mix it with water it will keep it sucked up until the air get so dry that it can no longer hold on to it and thus releases it a little at a time. 1 to 1 ratio = about 70%rh Here in Arkansas. It could differ in other climates.