Quick answer: For cardboard cat projects, avoid plastic packing tape, metal staples, hot glue strings, glossy printed boxes, spray paint and solvent glues. Use plain kraft boxes, gummed paper tape, wheat paste or non-toxic PVA glue, and water-based paints that are fully dry. Remove every staple and label before building and check the castle weekly.
Cardboard castles, hideouts and scratchers are among the best DIY projects for cats. Cats love boxes, and a well-made castle can look surprisingly smart in a living room. But a box is not automatically a safe toy. The tape, ink, staples and glue that come with packaging, or that we add when building, can cause real problems for a cat that chews, scratches and sleeps in it.
This guide covers what to remove, what to avoid and what to use instead, then shows how to keep a castle looking design-forward without unsafe finishes. If you think your cat has eaten something harmful, ASPCA Animal Poison Control can help.
Why safety matters with cardboard
Cats explore with their mouths. They chew corners, lick surfaces, and scratch until fibres come loose. A castle may also become a sleeping place, so the cat breathes and grooms in it for hours. Anything on or in the cardboard can end up being swallowed or inhaled. Small items like staples can cut, plastic tape can cause blockages, and some inks, glues and paints release fumes or contain chemicals you would not want a cat to eat.
Tapes to avoid and to use
| Tape | Risk | Verdict |
|---|---|---|
| Plastic packing tape | Chewed into strips; can block the gut | Avoid |
| Duct tape | Strong adhesive; plastic backing | Avoid |
| Double-sided tape | Sticks to fur and paws | Avoid |
| Masking tape | Paper backing; weaker | OK for light joins |
| Gummed kraft paper tape | Paper and plant-based glue | Best choice |
Strip all plastic tape from delivery boxes before building. It peels off more easily if you warm it slightly with a hairdryer. For your own joins, gummed paper tape (the kind you wet to activate) is strong and safe, and it looks neat.
Staples, clips and metal
Many boxes are stapled at the base. Staples are sharp and easily missed. Before building, run your hand carefully along every seam and use pliers or a staple remover to take them out. Check for metal clips, wire handles and plastic windows on product boxes, too.
Never use a stapler to build a cat castle. Use paper tape, glue or slot-together joints instead.
Inks, labels and coatings
Plain brown kraft cardboard is the safest. Heavily printed boxes, especially glossy or plastic-coated ones, are less ideal for cats that chew. Remove shipping labels, barcodes and plastic stickers. If a box has a shiny laminate, turn it inside out so the plain side faces the cat, or use it for parts the cat will not chew.
Avoid using boxes that held chemicals, cleaning products, pesticides or anything with a strong smell.
Glues: safe and unsafe
| Glue | Verdict | Notes |
|---|---|---|
| Wheat or flour paste | Safe | Free, slow to dry |
| Non-toxic PVA (white craft glue) | Safe once dry | Dry 24 hours |
| Hot glue | Use carefully | Remove thin strings; can be chewed |
| Super glue | Avoid | Fumes, hard sharp beads |
| Solvent or spray adhesive | Avoid | VOCs, fumes |
Let any glue dry fully, ideally 24 hours, in a ventilated room before the cat uses the castle. The EPA notes that many glues and paints release volatile organic compounds, so choosing water-based products and airing things out matters for cats and people alike.
Paints and finishes
Unpainted kraft cardboard looks clean and modern. If you want colour, use water-based, non-toxic paints such as children's poster paint or low-VOC wall paint, and let it dry completely for a day or two before the cat uses it. Avoid spray paint, oil-based paint, varnish and glitter.
Keep paint on the outside walls only. Inside surfaces, entrances and scratch areas should stay bare cardboard, as these are the parts cats chew and scratch.
A pre-build safety checklist
- Choose plain, clean, dry boxes with no strong smells.
- Remove all staples, clips and plastic windows.
- Strip all plastic tape and labels.
- Turn glossy surfaces inward or discard them.
- Plan joins with paper tape, paste or slots.
- Paint only with water-based, non-toxic paint on outside surfaces.
- Let everything dry and air for 24–48 hours.
- Check edges and openings for sharp corners and smooth them.
Design-forward finishing ideas
A cardboard castle does not have to look like a pile of boxes. Simple design choices make it look intentional and blend into a grown-up room.
- Stick to one tone: all kraft brown or one muted paint colour.
- Cut entrances as clean arches or circles using a plate as a template.
- Use gummed paper tape in a matching colour for neat seams.
- Keep the shape simple: stacked cubes or a single tall tower.
- Add a removable fleece pad inside for comfort; wash it weekly.
- Place it next to furniture with a similar tone, like oak or walnut.
For more ideas on blending cat items into a living space, see cat furniture that does not look like cat furniture, modern cat living rooms and modern cat furniture ideas. International Cat Care also explains why hiding places matter for cats' wellbeing.
Weekly checks once it's built
Check the castle once a week. Look for loose tape, chewed corners, damp patches, and any staple you might have missed. Repair with paper tape or replace the damaged box. If the cat has chewed and eaten pieces, remove the castle and watch for signs like vomiting, loss of appetite or straining in the litter box. Call your vet if any appear.
Cardboard castles usually last a few weeks to a few months depending on how hard the cat scratches. When it is worn, recycle it and build a new one. Keep a note of what wore out first, such as an entrance edge or a floor panel, and reinforce that spot with a double layer of cardboard and paper tape next time.
Also check the bedding. A fleece pad inside the castle collects hair, dander and sometimes fleas. Wash it weekly on a warm cycle with unscented detergent, and dry it fully before putting it back, because damp fabric on cardboard is a quick route to mould.
Scratching and cardboard
Many cats scratch cardboard castles, which is fine and even helpful. If you want to protect the castle, add a dedicated corrugated scratch pad at one entrance. For longer-lasting scratch surfaces, sisal is more durable. Our guides to whether sisal is safe for cats and cat furniture materials explain the options.
Room placement and ventilation
Where you build and where you place the castle matter too. Glue and paint in a well-ventilated room with a window open, and keep the cat out until everything is dry. Once finished, set the castle away from radiators, heaters and candles, since dry cardboard burns easily. Avoid placing it in direct strong sunlight for long periods, which can make some glues soft and smelly again.
A castle near the sofa or a window tends to get used most, because cats like to rest close to people or with a view. Put it on a rug or mat so it does not slide when the cat jumps in. If you have stairs or a shelf nearby, make sure the top of the castle cannot be used as a launch pad onto something unsafe.
Kids, crafts and safe supplies
Cardboard castles are a great project to make with children, but craft boxes often contain things that are dangerous for cats: glitter, sequins, pompoms, pipe cleaners, googly eyes, rubber bands and elastic thread. Set up a 'cat-safe' craft tray before you start with only paper tape, washable paint, plain paper and safety scissors. Do the decorating on the outside walls only, and check the floor afterward for dropped bits.
| Craft item | Cat-safe? | Swap for |
|---|---|---|
| Glitter | No | Painted dots |
| Googly eyes | No | Drawn-on eyes |
| Pompoms, yarn | No | Paper cut-outs |
| Pipe cleaners | No | Rolled paper strips |
| Washable paint | Yes, once dry | - |
For new owners setting up a home, our starter kit guide covers safe basics, and furniture for cats and humans shows where a castle can sit without taking over the room.
Cardboard cat DIY safety FAQ
Is hot glue safe for cat toys?
It is non-toxic once cool, but thin strings and beads can be chewed off. Remove strings, use it sparingly, and choose paper tape or paste where possible.
Can cats chew cardboard safely?
Light chewing of plain cardboard is usually fine. If your cat swallows pieces, supervise and talk to your vet.
Is printed cardboard toxic to cats?
Most packaging inks are low risk in small amounts, but plain kraft is safer, especially for cats that chew.
How long should paint dry before my cat uses a castle?
At least 24–48 hours in a ventilated room, until there is no smell.
