There are 9 Vessel Fragments in Hollow Knight. Every three you collect form one Soul Vessel and add more SOUL for spells and healing.
Vessel Fragments are the SOUL upgrades in Hollow Knight, the counterpart to Mask Shards. Per the wiki, three Vessel Fragments combine into one Soul Vessel that raises maximum SOUL by 33, and there are 9 Vessel Fragments in the game. All nine add three Soul Vessels, roughly doubling the SOUL the Knight can carry.
More SOUL means more spell casts and more healing before the meter runs dry. According to the wiki, SOUL fuels both the Focus heal and the offensive spells, so the 
extra Vessels are a direct power increase for spell-heavy and survival-focused builds alike.
The 9 fragments come from a mix of shop purchases, exploration finds, an Essence reward, and a Geo sink. Two are bought from 
Sly in Dirtmouth, which makes the first Soul Vessel one of the easier early upgrades to plan around.
This guide is the location list: every one of the 9 Vessel Fragments, the requirement attached to each, and a sensible order to collect them. In practice, front-loading the cheap and early fragments smooths out the mid-game, when SOUL starvation during boss fights is at its worst.
There are 9 Vessel Fragments in the base game. 3 Fragments = 1 Soul Vessel (+33 SOUL); all 9 add three Vessels. Two are bought from Sly in Dirtmouth for Geo.
The Ancient Basin fragment costs 3000 Geo dropped into a fountain.Per the wiki, three Vessel Fragments form one Soul Vessel, and each Soul Vessel raises maximum SOUL by 33. The base SOUL meter holds 99, so collecting all 9 fragments adds three Vessels and brings the total to 198, double the starting capacity.
According to the wiki, SOUL stored in Vessels fills the main meter automatically once there is room, so the extra capacity acts as a reserve for back-to-back heals or spells. One quirk: the Nail fills Vessels at a reduced rate of 6 SOUL per hit, though all other SOUL sources fill them normally.
Prioritize the two Sly fragments and the early exploration finds before the first hard boss. In actual play, an extra Soul Vessel is often the difference between landing a clutch heal and dying with an empty meter.
According to the wiki, the 9 Vessel Fragments are spread across Hallownest, from Dirtmouth's shop to the depths of the Ancient Basin. The table below lists every fragment with its location and the requirement that gates it. Sections after the table break the groups down in detail.
| # | Location | Requirement |
|---|---|---|
| 1 | Sly's Shop, Dirtmouth | Buy for 550 Geo after finding Sly |
| 2 | Sly's Shop, Dirtmouth | Buy for 900 Geo after the Shopkeeper's Key |
| 3 | Greenpath (near Queen's Gardens entrance) | Bottom room, on a platform by a Grub |
| 4 | Forgotten Crossroads (left of the lift) | Unlock the City of Tears lift |
| 5 | City of Tears (above King's Station) | Clear the battle arena to open the gate |
| 6 | Deepnest (above the working tram) | Cross the Garpede corridors |
| 7 | Stag Nest | Open all Stag Stations |
| 8 | Resting Grounds (the Seer) | Collect 700 Essence |
| 9 | Ancient Basin (the fountain) | Drop 3000 Geo into the fountain |
Two fragments are pure Geo purchases, four are exploration finds, one is an Essence reward, and one is a steep Geo sink. No single ability unlocks them all, but reaching the City of Tears opens the largest share at once.
Per the wiki, two of the 9 Vessel Fragments are sold by Sly in 
Dirtmouth. The first costs 550 Geo and is available as soon as Sly is rescued from the Forgotten Crossroads, making it one of the earliest SOUL upgrades in the game.
The second shop fragment costs 900 Geo, but according to the wiki it only appears after the Knight delivers the 
Shopkeeper's Key to Sly and has already bought the 550 Geo fragment. The key unlocks his expanded back-room stock, the same stock that carries the Elegant Key and two Mask Shards.
Because both are flat Geo purchases, they are the most reliable fragments to plan around. In practice, banking enough Geo to clear the 550 Geo fragment before the first real boss is one of the simplest ways to reach an early Soul Vessel.
Four fragments are found in the world rather than bought. Per the wiki, one sits in 
Greenpath, in the bottom room near the sealed Queen's Gardens entrance, on a platform beside a Grub. 
Isma's Tear makes the approach easier but is not strictly required.
According to the wiki, two more sit around the 
City of Tears: one left of the lift in the Forgotten Crossroads, reachable only after that lift is powered from the City, and one above King's Station behind a battle arena that must be cleared to open the gate. The fourth waits in 
Deepnest, above the working tram past a stretch of Garpede tunnels.
These four reward normal exploration of the mid-game regions, so they tend to fall into place as the Knight opens up Hallownest. In practice, the Deepnest fragment is the trickiest, since the Garpede corridors punish mistimed movement.
The last two fragments are the most demanding. Per the wiki, the 
Seer in the Resting Grounds hands over a Vessel Fragment once the Knight collects 700 Essence with the Dream Nail, a long-term goal that usually clears partway through a run.
The final fragment is a Geo sink. According to the wiki, it is found in the fountain in the Ancient Basin, and claiming it requires dropping 3000 Geo into the Pale King's fountain. The Geo is spent, not lent, so this is often the last fragment players collect once their wallet can spare it.
Together these two cap off the set. Since the extra SOUL feeds spells like 
Shade Soul and 
Abyss Shriek, a full set of Vessels is most valuable for the spell-heavy end-game and the hardest boss rematches.
The fragments are not missable, so order is about efficiency. This sequence front-loads the cheap SOUL and saves the slow goals for last.
In practice, most players have two full Soul Vessels well before the Essence and fountain fragments, so the third Vessel tends to be a completion-run goal rather than a mid-game milestone.
Vessel Fragments are one of two collectible upgrade sets, alongside Mask Shards. These spokes cover the connected items, spells, and keys.
Game data and screenshots adapted from hollowknight.fandom.com, used under CC BY-SA 3.0. Original content remains the property of the wiki contributors and Team Cherry.