Quick answer: A cardboard tunnel system for cats uses three to five moving boxes laid end to end, each with openings cut about 18 to 20 cm wide, joined by tucking flaps into each other rather than with loose tape. Remove staples and plastic first, add one taller lookout box with a peep hole, and check joints weekly for loose pieces.
Moving leaves you with a pile of sturdy boxes and often a cat unsettled by a new home. A cardboard tunnel system puts both to use. Cats like enclosed spaces where they can hide, ambush and explore, and a run of joined boxes gives them all three.
This build takes under an hour, uses no special tools and comes apart easily for recycling. It differs from a castle build, which stacks boxes upwards; tunnels stay on the floor and spread out.
Why Cats Like Cardboard Tunnels
Enclosed spaces help cats feel secure, and running through a tunnel uses the same stalking and pouncing behaviour as hunting. International Cat Care's guidance on playing with your cat describes play as an enjoyable part of domestic life for most adult cats. Tunnels add hiding places too, which is useful in a new home while a cat settles.
Cardboard is also easy to scratch, so many cats will claw at the edges. That is fine; it is a cheap scratching surface that will be recycled anyway.
Boxes and Tools for the Run
| Item | Spec | Notes |
|---|---|---|
| Moving boxes | 3 to 5, similar width, about 40 to 50 cm | Sturdy double-wall boxes last longer |
| Box cutter or strong scissors | Sharp blade | Adults only |
| Pencil and ruler | - | For marking holes |
| Paper tape (optional) | Water-activated or paper masking tape | Use only on outside seams |
| One taller box | For a lookout | Optional |
Prepare the Boxes Safely
Moving boxes collect staples, plastic tape, labels and marker ink. Remove staples with pliers, peel off plastic tape and shipping labels, and discard any box that is damp, mouldy or stained with chemicals. Our safety checklist for tape, ink and staples in cardboard builds covers what to remove before a cat plays with cardboard.
- Pull out every staple.
- Peel plastic tape and labels; plastic strips can be chewed and swallowed.
- Skip boxes that held cleaning products or chemicals.
- Let boxes air out if they smell musty.
Sizing the Openings
An opening about 18 to 20 cm wide and 18 to 20 cm high suits most adult cats; large breeds may need 22 to 25 cm. Cut openings in the ends of each box so they line up when boxes sit end to end. Add one or two side openings along the run so a cat has more than one way out and is never trapped.
Smooth cut edges by folding them inwards or running a finger along them. Rough cuts are not dangerous, but a neat edge lasts longer.
Building the Tunnel in Under an Hour
- Minutes 0 to 10: remove staples, tape and labels from every box.
- Minutes 10 to 25: mark and cut end openings in each box, lining them up.
- Minutes 25 to 35: cut one or two side exits along the run.
- Minutes 35 to 45: join the boxes by tucking flaps into each other.
- Minutes 45 to 55: add the lookout box at one end with a peep hole.
- Minutes 55 to 60: check for loose pieces and let the cat explore.
Joining Boxes Without Loose Tape
The safest way to join boxes is with their own flaps. Leave the end flaps on when cutting the opening, then tuck the flaps of one box inside the next so they overlap. Friction holds them together. For a firmer join, cut a slot in one flap and a tab in the other and slide them together.
If you must use tape, use paper tape only on the outside of seams, where the cat cannot reach the edge to chew it. Avoid plastic packing tape inside the tunnel.
Layout Ideas
| Layout | Best for | Notes |
|---|---|---|
| Straight run | Small rooms, a first try | Three boxes along a wall |
| L-shape | Corners | Two runs meeting at a box with two openings |
| T-junction | Two cats | A central box with three exits |
| Loop | Large rooms | Ends meet; no dead ends |
Run the tunnel along a wall rather than across a walkway, so people do not trip over it at night.
Adding a Lookout Box
A taller box at one end, with a peep hole near the top, gives the cat a place to sit and watch. Cut the peep hole about 8 to 10 cm across, at the cat's head height when sitting. Put a folded towel inside for comfort. Our cardboard castle and box enrichment hub has more ideas for raised boxes.
Play Ideas
- Drag a wand toy past an opening and let the cat ambush it.
- Roll a ball through the tunnel.
- Hide a few treats inside for the cat to find.
- Put a paper bag with the handles cut off at one exit for a crinkly surprise.
Keep wand toys and string away when you are not there. VCA Animal Hospitals notes that cats are known for swallowing thread, wool and small toys, and not all of them pass through safely.
Using a Tunnel in a Multi-Cat Home
With two or more cats, make sure the tunnel has several exits so no cat is cornered. A T-junction or loop is better than a straight run with one way in. Our cardboard castle build for multi-cat homes covers sharing in more detail.
Weekly Checks and Rotation
- Check joints for loose flaps or tabs.
- Remove any chewed pieces.
- Replace boxes that are soggy, torn or soiled.
- Move the tunnel or change the layout every week or two to keep it interesting.
Our guide to the cardboard castle rotation system shows how to swap boxes in and out so the cat stays curious.
When to Recycle the Tunnel
Cardboard does not last forever. Recycle the tunnel when boxes are flattened, soiled or heavily shredded. Keep a few spare boxes flat in storage so you can replace sections as they wear.
Our cardboard castle safety checklist has more checks for long-term cardboard builds, and International Cat Care explains how cat-friendly homes give cats places to hide and explore.
Helping a Cat Settle After a Move
A new home can make even confident cats wary for days or weeks. A tunnel set up in the cat's first room gives it a ready-made hiding place that smells of the old home, since the boxes travelled with you. Put a worn T-shirt or the cat's own blanket inside one section so the scent is familiar.
- Day 1: set the tunnel against a wall in the cat's base room, with food, water and litter nearby but not inside it.
- Days 2 to 4: let the cat use the tunnel to hide; do not pull it out.
- Once eating and exploring: start short play sessions at the tunnel exits.
- After a week or two: move part of the tunnel into the main living area to encourage exploring.
If the cat stays hidden for long periods, stops eating or avoids the litter box, call your vet.
Adding Scratching Spots to the Run
Many cats scratch inside or at the mouth of a tunnel. You can make the most of that by laying a flat corrugated cardboard pad at one exit, so the cat finishes a run with a stretch. Our guide to the best corrugated cardboard for a homemade scratcher explains which board cats prefer, and the DIY scratcher hub has sturdier builds once the tunnel wears out.
In a small flat, a tunnel can run behind the sofa or under a bed. Our small apartment cat home hub has more space-saving layouts.
Cardboard Tunnel Questions
How big should a cardboard tunnel opening be for a cat?
About 18 to 20 cm wide and high suits most adult cats. Large breeds such as Maine Coons may need 22 to 25 cm. Cut openings in the box ends so they line up, and add one or two side exits so a cat always has another way out.
Are moving boxes safe for a cat to crawl through?
Plain cardboard is generally safe once staples, plastic tape, labels and anything that held chemicals are removed. Discard damp or mouldy boxes. Check the tunnel weekly and remove chewed pieces, because some cats chew cardboard and swallowing a lot of it is best avoided.
How do I join cardboard boxes without tape?
Leave the end flaps on, then tuck the flaps of one box inside the next so they overlap and friction holds them. For a firmer join, cut a slot in one flap and a matching tab in the other and slide them together. Use paper tape only outside.
How many weeks will a box tunnel hold up?
Usually a few weeks to a few months, depending on how much the cat scratches and chews. Replace boxes that are soggy, torn, soiled or flattened. Keeping a few spare flat boxes makes it easy to swap sections and keep the tunnel going.
