How to pack chilli Powder
In a word, you can't.

The issue is with the bag vs. the bottle. Both are made out of (essentially) the same thing. But the bottle is thicker and 'breathes' less than the bag. In a word it is less porous.

Plastic bags are not good long term storage, especially ones you buy at the grocery store. What you need to do for maximum shelf life is (at least) a plastic bottle.

Me, I make chili powder every 6 - 8 months and store it in a glass container in my pantry. It stays reasonably fresh the whole time.

So the hierarchy of storage goes something like this.

Paper bags, plastic bags, plastic containers, metal/glass containers


With the left most items being more porous than the one to it's right.