Just got this reply from NjoY:
Hi Joshua,
Thank you for the kind words!
As for your question, the "wick" is actually made of cotton not polyester so there is nothing to worry about.
The liquid (aka "juice") turns the cotton a dark brownish color initially and becomes darker as the fluid is vaporized.
Hopefully this was helpful, however; if you have any other questions please feel free to ask!
Take care Joshua and have a great week.
Sincerely,
David
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well, that's relieving to know!