A food dehydrator is what i use. Not sure what kind of TPU you have, but when I first started using the Ninjaflex TPU I asked their support about humidity and they told me it does not affect the product. They said they take no precautions for humility and do not even ship in sealed bags.. I do not seal it up in air tight containers like all other filament and have no problems. What kind of TPU is it and what is the issue that is occurring?