yeah, exactly. At 140F 100grams will absorb 5-7 grams of water from the air. The more water you can absorb from the air, the lower the relative humidity is
Relative humidity is just a function of how much moisture air can hold based on temp.
If I have a box at 77f with 50% humidity and raise temp to 140F, relative humidity drops to 7.9%
This allows the filament to release it’s moisture.
As the box cools, the desiccant absorbs moisture faster, although it begins absorbing at 140 because the moisture from the filament increases relative humidity.
Here is some empirical evidence from my dry box.
Starting temp and humidity = 75F and 50% on hygrometer
at 140F with three fresh spools PETG =75%
after 24hours = 16%
after 24hours with heat off = 10%
Here are some equations to calculate relative humidity based on temp change:
you can use the magnus-tetens equation to calculate saturation pressure vapor and then relative humidity change for a given temp assuming an airtight container to verify my calculations for relative humidity
Saturation pressure = 6.1094 exp((17.7*T)/(T+233.04)
do this for both temps
Now you can calculate relative humidity, which is just the ratio of actual vapor pressure to saturation;
RH1 =E1/(Es(T1), or rearranged E1=RH1xEs(T1)
then calculate RH2 using the same equation since you now know E1, except use T2 or 140F in this case.