Quick Answer: Cube storage systems achieve 3-4x the storage density of conventional racking by eliminating aisles and stacking bins in dense grids. AutoStore leads the market with 1,250+ installations, offering the highest density. Exotec Skypod provides faster, more consistent retrieval but at lower density. Investment starts at $1M for small systems and scales linearly. Best suited for e-commerce, spare parts, and any operation where space is more expensive than speed.
The Cube Storage Revolution
Cube storage represents the biggest shift in warehouse storage technology since the invention of the pallet rack. By eliminating aisles — the single largest consumer of warehouse floor space — cube systems achieve storage densities that seemed impossible a decade ago.
In a conventional warehouse, 55-65% of floor space is consumed by aisles for humans and forklifts. Cube storage eliminates all of it. Every square meter of the grid footprint stores product.
How Cube Storage Works
The AutoStore Architecture
AutoStore — the pioneer and market leader with over 1,250 installations globally — uses a distinctive top-of-grid approach:
- The grid: An aluminum framework of vertical and horizontal rails forming a grid pattern. Bins stack vertically within the grid cells, up to 24 bins deep.
- The bins: Standard plastic bins (typically 449×649mm or 330×449mm) store inventory. Each bin has a unique ID.
- The robots: Battery-powered robots ride on top of the grid on rails. They lower a gripper mechanism through the grid to reach the target bin, lifting it out. If the target bin is buried under other bins, the robot temporarily relocates the bins above it (called "digging").
- The ports: Workstations at the grid edge where robots deliver bins to human pickers. After picking, the robot returns the bin to the grid — typically near the top, as frequently accessed bins naturally migrate upward.
Key design principle: AutoStore is optimized for density, not speed. Retrieving a bin at the top of the stack takes 10-20 seconds. Retrieving a bin buried 15 levels deep can take 2-5 minutes as the robot digs through layers. The system's intelligence compensates by pre-positioning high-velocity bins near the surface.
The Exotec Skypod Architecture
Exotec takes a fundamentally different approach:
- The racking: Standard-height racking structure (up to 12m) with bins stored on shelves at each level.
- The robots (Skypods): Compact robots that drive on the floor AND climb the racking structure vertically. A Skypod travels horizontally to the correct aisle, climbs to the correct level, extends a mechanism to grab the bin, and delivers it to a pick station.
- Direct access: Every bin is directly accessible without moving any other bins. No digging required.
Key design principle: Exotec trades some density for speed and consistency. Retrieval time is 1-2 minutes regardless of bin position — no variability based on storage depth.
Head-to-Head Comparison
| Factor | AutoStore | Exotec Skypod | |--------|-----------|---------------| | Storage density | 3-4x conventional | 2-3x conventional | | Bins per sq m | 8-16 (depending on grid depth) | 4-8 | | Retrieval time (best) | 10-20 seconds | 45-90 seconds | | Retrieval time (worst) | 2-5 minutes (deep bins) | 90-120 seconds | | Retrieval consistency | Variable (position-dependent) | Consistent | | Picks per station/hr | 200-400 | 250-650 | | Bin weight limit | 30 kg | 30 kg | | Max bin dimensions | 649×449×330mm | 600×400×350mm | | System height | 3.5-5.5m | Up to 12m | | Robot speed | 3.1 m/s horizontal | 4 m/s horizontal, 2 m/s vertical | | Robots per system | 10-200+ | 10-100+ | | Cost per bin position | $50-$120 | $80-$180 | | Installations worldwide | 1,250+ | 100+ |
When Cube Storage Makes Sense
The Ideal Profile
Cube storage delivers maximum ROI when your operation matches this profile:
- Space-constrained facility — When you're out of room and relocating or expanding is expensive. Cube storage fits 3-4x more inventory in the same footprint.
- Small-to-medium items — Products that fit in bins under 600×400×350mm and 30 kg. E-commerce, spare parts, electronics, cosmetics, pharmaceuticals.
- High SKU count — 5,000-500,000+ SKUs. Cube storage handles massive SKU diversity efficiently because every bin is independently accessible.
- Moderate-to-high order volume — 500-50,000+ orders per day. Below 500 orders, VLMs or carousels may suffice. Above 50,000, you may need multiple cube systems or shuttle AS/RS.
- Piece-level picking — Orders consisting of individual items picked from bins, not full cases or pallets.
The Economics of Density
The real ROI of cube storage often comes from space savings rather than labor savings.
Scenario: A 50,000 sq ft e-commerce warehouse at $12/sq ft annual lease, storing 40,000 SKUs:
| Metric | Conventional Racking | Cube Storage (AutoStore) | |---|---|---| | Storage positions | 15,000 | 45,000 | | Floor space used | 45,000 sq ft | 15,000 sq ft | | Annual lease cost (storage area) | $540,000 | $180,000 | | Pickers needed (2 shifts) | 24 | 8 | | Annual labor cost | $1,248,000 | $416,000 | | Annual operating cost | $1,788,000 | $596,000 |
With a $4M cube storage investment, the system pays back in under 3.5 years on combined space and labor savings of $1.19M annually.
Alternatively, the freed 30,000 sq ft could support additional cube systems, value-added services, or be subleased — further accelerating ROI.
Deployment Considerations
Floor Requirements
Cube storage grids are heavy. A fully loaded AutoStore grid imposes 1,500-2,500 kg/sq m on the floor — significantly more than standard racking (500-800 kg/sq m). Verify your slab can handle the load before committing. Floor remediation, if needed, adds $5-$15/sq ft.
Temperature and Environment
Most cube storage systems are rated for 2-35°C operation. They are not suitable for cold storage or freezer environments. Humidity must stay below 85% non-condensing. If your facility has significant temperature swings or humidity issues, discuss environmental controls with the vendor.
Ceiling Height
AutoStore grids are relatively low — 3.5-5.5m total height. This means cube storage works in facilities with standard 6-8m clear heights, but it doesn't exploit high-bay space the way crane AS/RS does. If you have 12m+ ceilings, Exotec Skypod uses the height more effectively.
Bin Standardization
Moving to cube storage requires fitting your inventory into standard bins. Products that are too large, too heavy, or oddly shaped need alternative storage. Most deployments store 60-80% of SKUs in the cube system and maintain conventional racking or shelving for oversize items.
Scalability
Both AutoStore and Exotec scale in three dimensions:
- More bins — Add depth (AutoStore) or racking bays (Exotec) for more storage
- More robots — Add throughput without infrastructure changes
- More ports — Add pick stations for more simultaneous pickers
This modularity is a significant advantage over crane AS/RS, where scaling means adding entire aisles.
Implementation Timeline
| Phase | Duration | Activities | |---|---|---| | Design and engineering | 6-10 weeks | Layout, bin analysis, throughput modeling, WMS integration design | | Manufacturing | 8-14 weeks | Grid/racking fabrication, robot production | | Installation | 6-12 weeks | Grid assembly, robot commissioning, port setup | | Integration and testing | 4-8 weeks | WMS connection, inventory loading, operator training | | Total | 6-10 months | From contract to go-live |
Small systems (under 10,000 bins) can be operational in 4-6 months. Large systems (50,000+ bins) typically take 8-12 months.
For help calculating your payback period, see our AS/RS ROI guide. Use the Robot Finder to explore cube storage options for your facility.
Frequently Asked Questions
What is cube storage?
Cube storage stores bins in a dense grid without aisles, with robots operating on or within the grid to retrieve specific bins. It achieves 3-4x the storage density of conventional racking. AutoStore and Exotec are the two leading platforms with fundamentally different approaches to bin access.
How does AutoStore compare to Exotec Skypod?
AutoStore uses top-riding robots that dig through stacked bins, offering the highest storage density (3-4x conventional) but variable retrieval times based on bin depth. Exotec uses climbing robots for direct bin access at any level, providing faster and more consistent retrieval times but at lower density (2-3x conventional).
What are the limitations of cube storage?
The main constraints are item size (bins max ~600x400x350mm), weight (30-35 kg per bin), temperature range (2-35°C), and floor load capacity requirements (1,500-2,500 kg/sq m). Not all inventory fits in bins — most deployments store 60-80% of SKUs in the cube system with conventional racking for oversized items.