Just crafting new armor sets isn't sufficient in Monster Hunter Wilds. Eventually, upgrading your existing gear becomes crucial to tackle tougher challenges. Here's how to obtain and utilize Armor Spheres in Monster Hunter Wilds.
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Obtaining Armor Spheres in Monster Hunter Wilds
Armor Spheres primarily come as quest rewards in Monster Hunter Wilds, meaning you'll earn them by completing both main story missions and optional quests.
After defeating Uth Duna for the first time during your playthrough, you'll begin receiving Armor Spheres as quest rewards. From that point forward, nearly all main and optional quests from Uth Duna onward will offer Armor Spheres.

To preview potential rewards, select any quest from your journal and press R1 to view the rewards list. Successful quest completions will grant your rewards on the results screen.
This system makes Armor Spheres relatively easy to farm. While progressing naturally through the story yields a steady supply, actively completing optional quests provides even more opportunities to stockpile them.
Armor Sphere Usage Guide

Armor Spheres serve as essential resources for enhancing your equipment. At any base camp, speak with Gemma the smithy and select the armor forging/upgrading option. Choose a piece of crafted armor and press R1 to access the Upgrade tab.
Select your desired armor piece, then expend Armor Spheres along with Zenny to perform the upgrade. Note that upgrade costs increase progressively as you enhance each piece to higher levels.
This covers everything about acquiring and using Armor Spheres in Monster Hunter Wilds. For more gameplay tips and information, be sure to explore The Escapist's additional guides.