So they have varying promo codes depending on how many items you buy.  I believe it should apply to anything on this page and can mix & match as needed.

They also mention that for every 10 spools purchased, they’ll include an extra “random” spool of filament.  A little odd and it won’t show up in your cart, so you’d definitely be taking a bit of a chance that they’ll honor it and that it will be something useful to you.

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Promo codes have spaces for whatever reason, make sure you include those:

BUY 5 GET 30% OFF code：Double Eleven30
BUY 10 GET 45% OFF code：Double Eleven45
BUY 15 GET 50% OFF code：Double Eleven50

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End prices really aren’t great unless you’re purchasing at least 10, some example prices below (assuming 50% off):

$11.50/kg Navy Blue/Army Green PLA

$11.99/kg PETG

$11.99/kg ASA

$12.99/kg Matte PLA

$17.50 Filament Dryer