Sealed glass is best — inert, airtight with a good seal, and it lets you inspect the threads before you buy; its one weakness, light, is solved by a dark cabinet or the opaque box it ships in. Tin is an acceptable second — opaque and airtight, though you can't see what you're buying. Plastic bag is the worst — it lets in light and oxygen and crushes threads. This is exactly why Raihan ships its saffron in sealed glass bottles inside an opaque burgundy gift box. If you receive saffron in a bag, transfer it to a sealed glass jar or bottle immediately.
Tin
Opaque, airtight, easy to seal. The traditional saffron container for a reason.
Amber glass
Beautiful, easy to see threads through. Slight light penetration — keep in a dark cabinet anyway.
Plastic bag
The worst of all worlds: not airtight after opening, not opaque, easy to crush. Transfer immediately.
