Expanding Reels Slots: How Reel and Grid Expansion Works
Expanding Reels change the size of the playable area. A game might add rows, make one reel taller, unlock positions that were already visible, or switch into a larger grid for a feature.
Quick answerIn an Expanding Reels slot, the playable layout gets bigger or more of it becomes active. That might mean extra rows, a taller reel, added reels or columns, or locked cells opening up. How the expansion starts, how far it can go and when it resets all depend on the game.
What are Expanding Reels?
Expanding Reels change the structure of the play area. A smaller active layout grows by gaining rows, reels, columns or playable positions.
The basic idea is simple, but games can get there in very different ways. In Cowboy Coins, an edge reel gains one extra position after it fills with special symbols. In Vikings, the whole play area changes from 5×3 to 7×5 when Raid Spins begin. Folsom Prison starts with only part of a larger lockable structure active, then opens additional cells during play.
The shared idea is that more playable space becomes active. The trigger and the final shape can be completely different.
How do Expanding Reels work?
Most examples can be understood as a simple before-and-after change: the game starts with a smaller active structure, something triggers the expansion, and the resulting layout has more playable positions.
The growth might happen once or in stages. It can affect the whole grid or just one reel. Sometimes new rows appear; sometimes an existing reel gets taller; sometimes positions that were locked become playable.
Mental 2 shows how localised the change can be. Its xWays feature reveals three symbols of the same paying type and increases the height of the affected reel, without requiring the whole grid to grow.
What can actually expand?
There is no single Expanding Reels shape. The change can affect one reel, several rows, the whole grid or positions that were already visible but inactive.
| Game | What changes | Example behaviour |
|---|---|---|
| Cowboy Coins | One edge reel | A filled special-symbol edge reel gains one extra position. |
| Folsom Prison | Locked reel positions | Previously inactive cells open inside a larger lockable structure. |
| Floridaman | Individual reel height | Mystery Splits can add 2 or 3 symbol positions to one reel. |
| Vikings | Whole play area | Raid Spins change the structure from 5×3 to 7×5. |
| Fire in the Hole 2 | Rows | Each qualifying collapse activates another row, up to six active rows. |
| Concrete Cowboys | Rows and columns | A collected Level Up symbol expands the grid by one row and one column. |
So Expanding Reels are broader than simply adding a row at the top. What matters is that the active reel or grid structure genuinely becomes larger.
What can trigger the expansion?
What causes the expansion is up to the individual game.
Cowboy Coins ties the change to a fill condition. When one of its special-symbol edge reels becomes completely filled, that reel extends by one position.
Floridaman uses a random trigger instead. Its Mystery Splits can activate in the base game or bonus and expand a reel by 2 or 3 positions.
Vikings expands at feature entry: Raid Spins switch the game from its 5×3 base structure to a 7×5 layout.
Other games link growth to continuing action. In Fire in the Hole 2, each collapse activates another row, although the collapse itself can be triggered by an ordinary win, an xBomb explosion or Wild Mining.
So “reels that grow after a win” is too narrow as a definition. Wins can trigger expansion, but so can feature entry, random events, collected symbols and other game-specific conditions.
How long does the larger grid last?
The larger layout can last anything from one spin to an entire feature.
In Floridaman, Mystery Split expansion is temporary. A reel can become taller for the current spin and then resets before the next one.
In Cowboy Coins, a filled edge reel can extend once and stays expanded for the remainder of the current Free Respin feature.
Vikings uses a feature-state change. The 7×5 structure remains in place throughout Raid Spins, then the game returns to its 5×3 base layout afterwards.
Fire in the Hole 2 resets more quickly. Its active rows can grow from three to six during the current collapse sequence, but a new paid spin begins again with three active rows.
There is no universal reset rule. Expansion might last one spin, one continuing sequence or an entire bonus feature.
Base game vs bonus and Free Spins expansion
Expanding Reels can appear in the base game, inside a bonus, or only when a feature begins.
The same visual idea can behave very differently depending on where it appears. Floridaman can use Mystery Splits in both base play and bonus play, but each expansion resets between spins. Cowboy Coins keeps its expanded edge reel for the remainder of the Free Respin feature. Vikings changes the whole reel structure for Raid Spins.
The presence of a larger grid during Free Spins does not make Free Spins part of the Expanding Reels definition. It simply tells you where that game’s expansion rule applies.
Expanding Reels and Ways to Win
Making the grid larger can change the number of active winning combinations in a Ways to Win game, but that is an interaction rather than the definition of Expanding Reels.
Folsom Prison starts with 16 ways from its initial active positions. As locked positions open, the playable reel area grows towards its full 4-6-6-6-4 structure and the number of available ways can increase.
Cygnus 2 gives another example. It begins with 4 rows and 4,096 ways; continuing Avalanche wins can add rows up to a maximum of 8, where the published ways ceiling reaches 262,144.
Grid growth can change a Ways count, but Ways are not required. Concrete Cowboys uses ELK’s CollectR pay mechanic, yet a collected Level Up symbol still expands the grid by one row and one column. The payout system and the expansion mechanic are separate.
Expanding Reels vs Cascading Reels
Cascading Reels and Expanding Reels can happen together, but they change different things.
A cascade removes or replaces symbols and then checks the resulting screen again. Expansion changes the size or active structure of the playable area.
Fire in the Hole 2 combines them. Its Collapsing Mine removes winning symbols and refills the grid, while each collapse can also activate another row. One rule explains the replacement sequence; the other explains why the grid itself is getting larger.
What is Win-Driven Reel Expansion?
Win-Driven Reel Expansion is a narrower form of the broader expansion family. Here, a qualifying win directly causes the playable structure to grow for the continuing sequence.
Cygnus 2 is a clear example: every new winning Avalanche adds another row, up to a maximum of 8 rows.
Not every expanding-reel feature is win-driven. Cowboy Coins grows when an edge reel fills, Floridaman can expand randomly, and Vikings changes size when Raid Spins begin.
Win-driven expansion is one route to a larger grid, not the definition of Expanding Reels as a whole.
Expanding Reels vs Expanding Symbols and Giant Symbols
These names sound similar, but they refer to different changes.
Expanding Symbols make a symbol grow across additional positions that already exist. The reel or grid itself does not need to gain new positions.
Giant Symbols occupy several existing positions at once, often as one oversized symbol spanning multiple cells.
Expanding Reels change the playable structure instead. New positions become active, or the active reel/grid dimensions increase.
Are Megaways slots the same as Expanding Reels?
No. A variable reel height or a Megaways label is not enough on its own to classify a game as Expanding Reels.
For Slotathon, the dividing line is a defined growth or unlock event that takes the game from a smaller active structure to a larger one.
A game can combine a variable-Ways system with a separate expansion event, but those are different properties.
What Expanding Reels do not tell you
A larger play area can change how a particular game works, but the mechanic does not tell you how the rest of the game is tuned.
Expanding Reels alone do not establish:
- RTP;
- volatility;
- hit frequency;
- maximum win;
- bonus frequency;
- whether the game uses paylines or Ways;
- whether more positions create more winning combinations;
- whether the mechanic benefits the player.
Those properties have to be checked separately for each game. The Expanding Reels label only tells you that playable space grows or becomes active.
Expanding Reels FAQ
What are Expanding Reels slots?
Expanding Reels slots make the playable layout larger or activate extra positions. A game might add rows, make one reel taller, add reels or unlock cells that were previously inactive.
How do Expanding Reels work?
A smaller active layout grows after a game-specific trigger, leaving more playable positions active. How far it can grow and how long it stays expanded depend on the game.
Can only one reel expand?
Yes. Mental 2 and Floridaman both provide examples where an individual reel can become taller rather than the whole grid expanding at once.
Do Expanding Reels stay expanded?
Not always. Floridaman resets its Mystery Split expansion between spins, Cowboy Coins can keep an expanded edge reel for the rest of a Free Respin feature, and Vikings keeps its larger 7×5 structure during Raid Spins before returning to 5×3.
Can Expanding Reels happen in Free Spins?
Yes. Some games change the playable structure for a bonus or Free Spins state, while others use expansion in the base game or in both modes. The scope is game-specific.
Are Expanding Reels the same as Cascading Reels?
No. Cascades remove or replace symbols and re-evaluate the screen. Expanding Reels add or unlock playable positions. A game can use both mechanics together.
Are Expanding Reels the same as Expanding Symbols?
No. Expanding Symbols grow across positions that already exist. Expanding Reels change the active reel or grid structure itself.
Are Megaways slots the same as Expanding Reels?
No. A Megaways label or variable reel height is not enough on its own. Slotathon uses the Expanding Reels label when the evidence shows a defined growth or unlock event from a smaller active structure to a larger one.
Do Expanding Reels always increase the number of Ways?
No. Some Ways games gain more active combinations when the grid grows, but Ways are a separate payout system. Expansion can exist without Ways, and any change in the published Ways count is game-specific.
Sources reviewed
The examples on this page were checked against primary material wherever possible. Linked game names below lead to the software provider’s public game page where one was available. The evidence reviewed may also include in-game rules, developer game sheets and authenticated developer material that is not publicly accessible.
AvatarUX
NetEnt
Nolimit City
Pragmatic Play
ELK Studios
How we research slot mechanics
Slotathon starts with primary evidence such as game rules, in-game help, developer documentation and game sheets. Third-party reviews are used as secondary sources to compare against that evidence and help identify areas that may need further verification.
When sources disagree, we preserve the disagreement in the research instead of quietly choosing whichever version is easiest to publish.