Quick answer: A flat-pack tunnel system for an apartment is a set of square cardboard segments, about 25 × 25 cm inside and 50 cm long, joined with interlocking tabs rather than tape. Each segment folds flat when you unhook it, so the whole tunnel slides under a sofa or bed. Add peek holes and one corner piece, and supervise early sessions.
Cats love tunnels, but a fabric play tunnel takes up a strip of floor permanently and a cardboard one usually ends up as a taped-together lump that is too awkward to store. In a small apartment, the best tunnel is one that is out when the cat wants it and gone when you need the floor back.
This flat-pack design is part of our cardboard enrichment hub and our small-apartment cat home hub. At CozeCats we designed it around one rule: no tape, no glue, so every piece can fold flat and be reused or recycled.
Materials for a Flat-Pack Tunnel System
- Three or four large, clean double-wall cardboard boxes, with labels and tape removed.
- A long metal ruler and a pencil.
- A sharp craft knife and a cutting mat, used by an adult.
- A blunt butter knife or empty ballpoint pen for scoring fold lines.
- Optional: a small paper bag for a crinkle insert.
Double-wall cardboard holds its shape far better than single-wall, especially when a cat jumps on top. Check the boxes for staples and heavy ink; our guide to tape, ink and staples to avoid explains what to remove.
Segment Dimensions
Each straight segment is one long rectangle that folds into a square tube, with a narrow glue-free overlap that slots into itself.
| Part | Flat size | Folded size | Notes |
|---|---|---|---|
| Straight segment | 106 × 50 cm | 25 × 25 × 50 cm tube | 4 faces of 25 cm plus a 6 cm locking flap |
| Corner piece | Cut from two segments | 25 × 25 cm L-turn | Lets the tunnel change direction |
| End cap (optional) | 35 × 35 cm | Square with 5 cm tabs | Closes one end for a hideaway |
For a large cat, scale the inside to 30 × 30 cm; the flat size becomes 126 × 50 cm. Most domestic cats move comfortably through 25 cm, but a cat should never have to squeeze.
Cutting Tab Joints Instead of Tape
Tabs let segments hook together and unhook again without damaging the cardboard.
- On one end of each segment, cut two 5 cm wide tabs, 4 cm long, on opposite faces.
- On the other end, cut matching 5 cm slits, 1 cm in from the edge.
- Score all four fold lines along the length so the tube folds cleanly.
- Fold the segment into a square, tuck the 6 cm locking flap inside and push it under the opposite face.
- Join segments by sliding the tabs of one into the slits of the next.
Round every cut corner slightly and run a finger along each edge to check for sharp burrs. If a joint feels loose, add a third tab on the top face.
Peek Holes and Exits
A tunnel with only two openings feels like a trap to some cats. Cut one round peek hole about 10 cm across on the side or top of every second segment, at least 10 cm from any joint so it does not weaken the tab.
Peek holes give the cat a way to watch the room and a place for you to dangle a wand lure. Keep at least one segment without holes, which becomes the cat's preferred hiding spot. International Cat Care's guide to cat-friendly homes explains why cats value places where they can hide and still observe.
Layouts for a Small Room
| Layout | Pieces | Best place |
|---|---|---|
| Straight run | 3 segments | Along the back of a sofa |
| L-shape | 2 segments + corner | Around a coffee table leg |
| U-turn | 3 segments + 2 corners | Open floor during play only |
| Hideaway | 1 segment + end cap | Beside a radiator or bed |
Change the layout every few days so the tunnel feels new. Avoid placing it across a walkway, where someone could step on it in the dark. For more apartment cardboard builds, see our apartment cardboard castle.
Folding It Away
Unhook the tabs, untuck each locking flap and fold every segment flat along its scores. A four-segment tunnel stacks to a pile about 5 cm thick and 50 cm wide, which fits under most sofas and beds.
Store the pile flat and dry. Cardboard that gets damp warps and loses strength, so a cupboard is better than a balcony. Fold carefully along the same creases each time to keep the corners crisp.
Making the Tunnel a Play Session
A tunnel on its own gets a quick look. A tunnel with a game in it gets used for weeks.
- Drag a wand lure slowly past the entrance, then through a peek hole.
- Drop a crinkly paper ball inside one segment.
- Hide a few kibbles in the closed hideaway end.
- Finish a session at a scratcher by the tunnel exit.
International Cat Care's guide to playing with your cat has more on letting a cat stalk and pounce. Our indoor enrichment ideas list other games that work in small spaces.
Getting a Cautious Cat Into the Tunnel
Not every cat walks straight in. A shy cat may sniff the entrance for days before going through, and that is fine. Start with a single segment, open at both ends, so the cat can see daylight on the other side.
- Day 1: leave one open segment on the floor near where the cat rests.
- Day 2: put a few treats just inside each end.
- Day 3: place treats in the middle and drag a wand lure past one end.
- Day 4 onward: add a second segment once the cat walks through the first without hesitating.
Never push or carry a cat into the tunnel, and do not block either end while it is inside. A cat that feels trapped once may avoid the tunnel for a long time. Rub the inside with a cloth the cat has slept on to give it a familiar scent.
When to Replace Segments
Cardboard is meant to wear out. Replace any segment that is soggy, crushed, chewed through or has torn tabs. Because the segments are separate, you only need to make one new piece rather than rebuild the tunnel.
Keep a spare flattened box behind the sofa so you can cut a replacement in ten minutes. Recycle old pieces with your normal paper recycling.
Safety Checks for Cardboard Tunnels
Supervise the first few sessions to see how your cat uses the tunnel. Some cats chew cardboard; if yours swallows pieces, keep the tunnel for supervised play only. Never add string, ribbon or elastic to the tunnel, and check that no tape or staples are left anywhere on the cardboard.
With kittens or very young children in the home, keep the tunnel on the floor rather than raised, and check joints before every session. Our kids and cats cardboard build has tips on making it a family project safely.
Flat-Pack Cardboard Cat Tunnels
How big should a cat tunnel be inside?
About 25 × 25 cm inside suits most domestic cats, letting them walk through without crouching too low. For large breeds such as Maine Coons, scale it up to around 30 × 30 cm. A cat should never have to squeeze through a tunnel, so measure your cat at the shoulder if in doubt.
How do I join cardboard tunnel pieces without tape?
Cut two tabs on one end of each segment and matching slits on the other end of the next segment, then slide the tabs into the slits. Score fold lines so each tube holds its square shape. The joint holds during play and comes apart easily when you want to fold the tunnel away.
Is a cardboard tunnel safe for cats?
A cardboard tunnel is generally safe when it is made from clean, plain cardboard with tape, staples and heavy ink removed. Supervise early sessions, keep string and ribbon out of it, and replace any piece that becomes soggy, crushed or chewed. Keep it out of walkways to avoid trips.
How do I store a cat tunnel in a small apartment?
With a flat-pack design, unhook each segment, untuck the locking flap and fold it flat along the scored lines. A four-piece tunnel folds into a stack about 5 cm thick that fits under a sofa or bed. Store it dry, because damp cardboard warps and weakens.
How long will a flat-pack cardboard tunnel segment last?
It depends on the cat. A gentle cat may use the same segments for months, while an enthusiastic chewer can wear one out within weeks. With separate segments, you only need to remake the worn piece, so keep a spare flattened box ready for replacements.
