You can no longer buy them to use for upgrades. Instead, any leftover stacks in your inventory can only be "sold" to at the Tower for small amounts of Glimmer. Historical Context and Usage

In their prime, Helium Filaments were more than just a currency; they were the "fuel" for progression.

: In Destiny 2: Shadowkeep , players could use them to play a physics-based mini-game near Eris Morn on the Moon, which could even grant a hidden Triumph.

: Described as filaments of helium-3 fusion fuel, they were canonically gathered from lunar regolith and used to power everything from individual fusion rifles to the Last City itself.

The exchange rate was typically for 20 Helium Filaments . Destiny 2 (Pre-Deprecation) :

Players could buy them at the from the Vanguard Quartermaster or Crucible Quartermaster .

The methods for buying these filaments shifted significantly over the franchise's history: :

In the Destiny universe, were a vital planetary resource found on the Moon, essential for upgrading gear. While traditionally harvested in the wild, players could also "buy" them through various vendor exchanges depending on the game version. The Evolution of Purchasing Helium Filaments