In Oblivion, the Feather effect is an Alteration school spell that decreases your current encumbrance by reducing the weight of the items you are carrying, effectively increasing your total carrying capacity for the duration of the effect. However, it does not directly increase your maximum carry weight; instead, it lowers the effective weight of your inventory items, making you less encumbered
. The mechanics work such that Feather reduces your current carried weight by a certain number of points for a set duration. If the Feather effect would reduce your weight below zero, it only reduces it down to zero and no further. This means casting Feather when you are already lightly loaded has little to no effect. The best use is to cast Feather when you are already carrying a heavy load, as it then reduces the actual weight of what you carry, allowing you to move more freely
. Additionally, Feather effects do not automatically apply to items picked up after casting. To update the effect for newly acquired items, you need to dispel and recast the spell. Multiple Feather spells with different names can stack, increasing the total reduction in carried weight. Combining Feather with Fortify Strength spells or effects is an effective strategy to maximize carrying capacity
. In summary, Feather in Oblivion reduces the effective weight of your current inventory, allowing you to carry more items temporarily by lowering your encumbrance rather than increasing your base carry limit directly
