[SeanGAR]

Propylene glycol and polyethylene glycol are absolutely not the same thing.

Propylene glycol is 3 carbons long with 2 hydroxyl groups, weighing 76 g/mole.

Polyethylene glycol is a polymer of variable lengths and molecular weights.

Polyethylene glycol 200 weighs ~200 g/mole and is liquid at room temperature while polyethylene glycol 20,000 is ~20,000 g/mole and is a white solid at room temperature. They differ in how many ethylene glycol molecules are in the polymer. Miralax is polyethylene glycol 3350, weighing (you guessed it) 3350 g/mole.

PEGs are different from ethylene glycol, which is the poisonous component of antifreeze (PEGs are ethylene glycol polymers).

You want propylene glycol if you're mixing for humidity control, but I prefer and recommend beads.

Bovedas are OK ... they use saturated salt solutions to control humidity the way we use saturated sodium chloride to test hygrometers (at 20-25 C, NaCl --> 75% humidity, NaBr --> 58-59% humidity). I forget what salts Boveda uses.