For light, dry things near the top of a stack, yes: a clean, sturdy free box with no damp, smell or food history is fine, for a stay of weeks or of months. For heavy things, fragile things, the bottom layer of any stack and anything that has held food, use new double-wall boxes, however long you're storing. The longer the stay, the more that matters, because cardboard weakens the longer it carries weight. Our own packing advice is to avoid single-walled or grocery store boxes for anything fragile or heavy. Our double-wall boxes cost £3.50 to £5.25 each bought singly, or £2.50 to £4.50 a box in packs of ten (medium £25, large £35, extra-large £45), and our moving kits hold 10, 25 or 40 boxes for £35, £99.99 or £195.
When a free box is good enough, and when it isn't
On moving day a box only has to last a few hours in a van. In a storage unit it may carry four others for months. That is the difference that matters.
There's no set number of weeks after which a free box stops being good enough. What decides it is how much weight the box carries, how long it carries it, and whether it has been damp. The same rule applies to a three-week gap and a four-month stay: the stay just gives weight and damp more time to work.
| What's going in | Free box? | Why |
|---|---|---|
| Bedding, cushions, clothes, soft toys, near the top of a stack | Yes, if clean, dry and sturdy | Little weight inside it and little on top of it |
| Books, kitchenware, tins, tools | No, use a medium double-wall box | Heavy contents crush weak boxes, and the box has to be lifted again |
| Anything fragile | No, use double-wall | Wrapping protects the item; a strong box stops it being crushed |
| The bottom layer of any stack | Only if it is double-wall and still stiff; new is safer | It carries every box above it, for as long as you store, and a used box has already been loaded once |
| A box that held fruit, veg, meat or fish, or still smells of it | No, for anything | Crumbs and smells draw pests, and a smell carries |
| A long stay, many months or more | Only for light things on top; double-wall for anything carrying weight. Plastic crates are an option for clothes and bedding | Cardboard loses stacking strength the longer it's loaded |
Three things weaken cardboard over time, and a free box may have met all three. Damp air lowers a box's strength to resist crushing. Long periods under load cause what packaging testers call fatigue, so a stack that stands up in week one can sag later. And rough handling weakens a box, and a free box has already been through at least one move or delivery.
Pests are the other reason. Cardboard boxes give cockroaches the dark, undisturbed shelter they look for, and cockroaches can arrive in delivery boxes. Our storage terms don't allow food unless it's packed so it can't attract vermin, or anything that gives off odours (clause 18). An empty produce box isn't food, but it can bring the same crumbs and smells into your unit, so leave it out.
Our units are clean, dry and secure, but we don't offer climate control. Your belongings are stored at your own risk, including damage and deterioration (clause 30), and must be insured while they're with us (clause 31), either through our contents protection or through your own policy (do I need insurance for my unit?). If you'd be relying on that cover when a box collapses or gets damp, check what your policy says about that kind of damage; a sound box is the simpler protection.
How to check a free box
- Look at the cut edge. Single-wall board has one wavy layer between two flat sheets. Double-wall has two wavy layers, and resists crushing better.
- Press a corner. If it folds easily in your hand, it will fold under a stack.
- Look and sniff. Pass on water marks, stains, spots of mould, or any smell of damp or food.
- Check the wear. Crushed edges, torn flaps and layers of old tape mean the box has been knocked about.
- Close the flaps. The top has to close flat, or the box above it has nothing to sit on.
Then pack it full. Our guide to packing a storage unit for a house move explains why: a half-filled box compresses under weight and the stack above it leans. The same guide suggests keeping stacks to five boxes high unless the bottom boxes are rated for more, and using boxes of the same size so the faces line up.
When to buy double-wall boxes, and what ours cost
Every box we sell is double-walled. Prices are as listed in our shop in September 2026:
| Box | Size (mm) | Single | Pack of 10 | Best for |
|---|---|---|---|---|
| Medium | 457 × 330 × 330 | £3.50 | £25 | Books, kitchenware, tools: heavy things in a box you can still lift |
| Large | 450 × 450 × 500 | £4.50 | £35 | Clothes, bedding, bulky light things |
| Extra-large (tall) | 450 × 450 × 750 | £5.25 | £45 | Lamps, linen, awkward shapes |
The large and extra-large boxes share the same 450 × 450mm base, so they stack in straight columns. The medium box has a different base (457 × 330mm), so it won't line up under them. Put the heavy medium boxes at the bottom as one full, level layer, packed side by side, and stand the larger, lighter boxes on that layer rather than on a single medium box. Our packing guide's rules point the same way: weight low, and same-size boxes together, because mixed sizes make unstable piles.
You don't have to choose all or nothing, whether you're storing for three weeks or a year. Use new medium boxes for the heavy things and the bottom row, and your best free boxes for soft things on top. Ten medium boxes are £25.
If you're storing for many months or longer, while you downsize, work abroad or hold an estate, the same mix works, but check your free boxes harder and don't let any of them carry weight. Plastic crates are an option, not a must: our guide suggests them for clothes, bedding and soft furnishings on a longer stay, where moisture is the concern, because they close securely and are waterproof to a point.
Papers are heavy, so pack them in medium boxes and keep those in the bottom layer. Stand them on a pallet if you have one, as our packing tips suggest for furniture, and if damp is a worry the same reasoning makes a lidded plastic crate an option for papers too. Important documents are a different matter: our storage terms don't allow currency, deeds or securities to be kept in a unit (clause 18(i)), so keep those with you or with a solicitor or bank.
For crockery and glass, wrap each piece and use medium boxes. The Box Shop sells white packing paper (2.5kg, £9.99) and bubble wrap (500mm × 10m, £6.99, or 750mm × 25m, £14.99).
If you're a student storing a room over the summer, the Student Moving Kit is 5 medium and 5 large double-wall boxes, with tape and a marker pen, for £35. For a whole home, the Standard Moving Kit (£99.99) has 25 boxes, and the Large Moving Kit (£195) has 40; both add tape, a marker pen and bubble wrap. Our guide to how many boxes you'll need matches kits to home sizes.
Where to find free boxes worth taking
The best free boxes are proper moving boxes from someone who has just unpacked. Freegle, a UK charity for giving and getting things locally for free, is a good place to ask, as are local community groups. If you work in an office, ask for printer-paper boxes: they're small, which suits books. Supermarkets and local shops will sometimes hand over boxes if you ask, but that's up to each store, and most are produce boxes: fine for the van, not for your unit.
Get your boxes
When you know how many free boxes you'll use, fill the gaps from our online Box Shop, delivered to your door. If you still need a unit, get a price online or call us on 0800 2545585.
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