Doubling
If there are multiple doubling affixes, they will be calculated independently and will not affect each other.
This type of stat refers to things like "Dropped Fluorescent Memories have a X% chance to be doubled," "Dropped Fluorescent Memories have a X% chance to be tripled," etc.
The doubling of drops is only applied in the very last step of the drop calculation after accounting for all other drop stats.
Note: If there are multiple doubling affixes, they will be calculated independently and will not affect each other.

Calculation
Example 1: With the affix "There is a 100% chance for dropped Flame Sand to be doubled," when the drop is Flame Sand x1, the final drop will be Flame Sand x2 (Flame Sand x1 + Flame Sand x1)
Example 2: With the affix "There is a 100% chance for dropped Flame Sand to be tripled," when the drop is Flame Sand x1, the final drop will be Flame Sand x3 (Flame Sand x1 + Flame Sand x2)
Example 3: With both "There is a 100% chance for dropped Flame Sand to be doubled" and "There is a 100% chance for dropped Flame Sand to be tripled," when the drop is Flame Sand x1, the final drop will be Flame Sand x4 (Flame Sand x1 + Flame Sand x1 + Flame Sand x2)