# How to Make a Time Capsule

> To make a time capsule, choose an opening date and the person responsible for it, pick a sealed container made of stainless steel, aluminium or a stable plastic, fill it with things that last — letters on acid-free paper, black-and-white prints, small objects of metal, glass or ceramic — and keep it somewhere dry and indoors rather than in the ground. Then write down where it is and tell more than one person, because a capsule nobody remembers is as lost as one that rotted.

Making a time capsule is easy. Making one that is still there, still dry and still readable on the day it opens is a small conservation project.

What follows is drawn from the guidance conservators publish — the Library of Congress and the Smithsonian's Museum Conservation Institute both have pages on exactly this — turned into something a family, a class or a club can do in an afternoon.

_Updated September 20, 2026_

## How to make a time capsule, step by step {#steps}

Six decisions, in the order that saves you from redoing any of them.

- **1. Choose the date and the opener** — Decide when it opens and who is responsible for opening it before you buy anything. Everything else — the container, the contents, where it lives — depends on how long it has to last.
- **2. Choose the container** — Stainless steel, aluminium or a stable plastic, with a lid that screws down onto a gasket. Slightly larger than what you plan to put in it.
- **3. Choose contents that last** — Paper, pencil, black-and-white prints, metal, glass, ceramic. Leave out anything that rots, leaks, gives off fumes or needs a machine to be read.
- **4. Pack it** — Each item in its own envelope or bag, the heaviest at the bottom, nothing loose. Add silica gel, and a list of what is inside and why.
- **5. Decide where it lives** — Indoors and dry beats underground every time. A cupboard, a loft or a wall cavity will outlast a hole in the garden.
- **6. Make it findable** — Write down where it is, tell several people, and put the opening date somewhere that will still be read in twenty years.

## Start with the date, not the box {#date}

The tempting mistake is to choose a container first. The date decides almost everything: a capsule that opens in five years can be a good tin in a cupboard, while one that opens in fifty is a different object with different rules.

For a family, a class or a club, five to twenty-five years is the useful range. It is long enough for the contents to have become strange, and short enough that someone who sealed it will be there to open it — which is most of the pleasure.

Longer than that and you are writing to strangers. That is a fine thing to do, but it is an institution's job: a school, a town hall or a company can plausibly still exist and still remember. A household usually cannot.

Whatever you choose, tie it to a date that will be remembered anyway — a birthday, an anniversary, a graduation year — and name the person, or better the role, responsible for opening it.

## Which container survives {#container}

A time capsule is a closed atmosphere. The container's job is to keep water, air and light out, and not to add anything harmful of its own.

|  | Use | Avoid |
| --- | --- | --- |
| Material | Stainless steel, aluminium, or uncoated polyethylene or polypropylene — the plastics marked with recycling codes 1, 2 and 5 | PVC pipe, bags or boxes. PVC is chemically unstable and releases acid as it breaks down, inside a sealed space |
| Seal | A screw-down lid with a gasket; for a metal capsule meant to last decades, a welded seam | Soft solder, which fails underground and lets water in, and any kind of tape |
| Humidity | Silica gel sachets added just before sealing, to buffer the moisture trapped inside | Sealing it on a damp day with nothing inside to absorb the moisture |
| Size | A little larger than the contents, packed so nothing rattles, with the heaviest items at the bottom | A biscuit tin, which rusts, or a cardboard box, which is acidic and soaks up water |
| Marking | The opening date and which way is up, written on the outside | An unmarked container that looks like rubbish to whoever finds it |

These recommendations follow the published guidance of the Library of Congress and the Smithsonian's Museum Conservation Institute. Purpose-made stainless steel capsules exist, and are worth it for anything meant to last more than twenty years.

## What to put in a time capsule {#contents}

Favour things that have already proven they last. The safest materials are the oldest ones: paper, carbon, metal, glass, stone.

### Things that last

- Letters written in pencil or pigment ink on acid-free paper
- Black-and-white photographic prints, which outlast colour ones
- Coins, keys, badges and other small objects of non-corroding metal
- Something made of glass, ceramic or stone
- A printed page of everyday prices: bread, a bus ticket, rent, a phone
- Textiles of plant fibre, such as cotton or linen

### Things that tell the story

- A letter from each person, addressed to whoever opens it
- Predictions about the year it opens, signed and dated
- An ordinary day, written down hour by hour
- A hand-drawn map of the street, the school or the house as it is now
- The front page of a newspaper, photocopied onto acid-free paper rather than clipped
- A list of everyone who took part, and how to find them

### The contents list

- Every item, what it is, and what it is made of
- Why each one was chosen — the part the finder will actually want to read
- A second copy of the list kept outside the capsule, with the opening date

Pack each item, or each group of similar items, in its own acid-free paper envelope or a sealable polyester or polyethylene bag. Separation matters: in a sealed box, one item that breaks down takes its neighbours with it.

## What destroys a time capsule from the inside {#avoid}

Water from outside is only half the risk. The other half is whatever you seal inside: in a closed box, one unstable item damages everything around it.

### Food, plants and anything organic

It decomposes, and it does so into the same air as your letters. That includes sweets, flowers, a lock of hair and the traditional slice of wedding cake.

### Rubber, wool and untreated wood

Rubber perishes and releases sulphur; wool contains it too; wood, oak especially, gives off acid vapour. All three corrode metal and mark paper.

### Newspaper clippings

Newsprint is too acidic to survive, and it yellows whatever it touches. Photocopy the page onto acid-free paper and keep the copy instead.

### Tape, glue and laminate

Pressure-sensitive tape fails and stains — including tape sold as archival — and lamination cannot be undone. Use folders and envelopes instead.

### Batteries and devices

Batteries leak. And a phone, a tape or a memory card is only as good as the machine needed to read it, which is the first thing to disappear.

### Colour prints and digital media

Colour dyes fade in a way black-and-white prints do not, and both conservation guides advise against relying on anything that needs today's hardware or software to be opened.

## Where to keep it, and why not to bury it {#where}

Burying a time capsule is the tradition, and it is the weakest option you have. Soil is wet, seals fail slowly, and a container that is fine after five years can be full of water after twenty. The International Time Capsule Society's own advice is that burial is a bad idea for paper.

The second problem is that buried things are forgotten. Gardens are re-landscaped, schools are rebuilt, the person who knew the spot moves away. The Society puts it bluntly: capsules are usually lost through thievery, secrecy or poor planning.

Indoors and dry is better on every count: a high cupboard, a loft that does not swing between hot and cold, a cavity in an interior wall, a cornerstone on the sheltered side of a building, a safe-deposit box. The capsule loses some romance and gains decades.

If it has to be buried, do it properly: dry, well-drained ground; a sealed steel capsule inside a second enclosure; a permanent marker above it; and the exact position — measured from two fixed points, with GPS coordinates — written down and kept somewhere else.

## Make sure somebody opens it {#found}

A capsule nobody remembers is as lost as one that rotted. This is the step that gets skipped.

### Tell more than one person

A secret capsule is a lost capsule. Tell the family, the class, the committee — and tell someone younger than you.

### Put the date where it will be read

A plaque on the wall, a note kept with the deeds or the will, a recurring entry in a shared calendar. One of them will survive.

### Register it

The International Time Capsule Society keeps a registry of capsules, with their location and opening date, so that a record exists outside your own household or organisation.

### Label the outside

The opening date, which way is up, and who to contact. Whoever finds it should be able to tell at a glance that it is not rubbish, and that it is not yet time.

## Where a digital time capsule fits {#digital}

Everything above is about objects. Two things a box handles badly — video and sound, and remembering its own date — are the two things a digital capsule is for.

|  | Physical capsule | Digital capsule |
| --- | --- | --- |
| Holds | Objects, paper, prints — things you can hold | Photos, video, voice recordings, documents and long text |
| Opening | Someone has to remember it, find it and open it | Unlocks on its date by itself, and emails the people you chose |
| Who can be there | Whoever is in the room | Any number of recipients, anywhere |
| Condition | Depends on the container, the damp and the contents | Files come out as they went in, in standard formats |
| Weak point | Being forgotten, or flooded | It depends on a company still operating. Ours publishes what it commits to, and what it does not |

They do different jobs, and plenty of people do both: the tin for the objects, and a digital capsule set to open on the same day with the voices, the video and an account of what was actually going on.

[What a digital time capsule is, and how ours works](https://time-capsule.io/digital-time-capsule.md)

## Related reading {#related}

- [How we preserve digital capsules](https://time-capsule.io/preservation.md) — Where the files live, what we commit to, and what we refuse to promise.
- [A family time capsule](https://time-capsule.io/family-time-capsule.md) — What to record of a household at one moment: voices, recipes, the ordinary week.
- [A graduation time capsule](https://time-capsule.io/graduation-time-capsule.md) — How a class capsule is actually organised, and which reunion to open it at.

## Time capsule questions {#faq}

### How long should a time capsule stay sealed?

For a family, a class or a club, five to twenty-five years: long enough for the contents to feel strange, short enough that someone who sealed it is there to open it. Longer spans suit institutions that can expect to still exist, and still remember.

### What is the best container for a time capsule?

A stainless steel or aluminium container with a gasketed screw lid, or a stable plastic such as polyethylene or polypropylene (recycling codes 1, 2 and 5). Avoid PVC, which releases acid as it breaks down, and add silica gel before sealing.

### Should I bury my time capsule?

Preferably not. A buried capsule is exposed to moisture and easily forgotten, and the International Time Capsule Society calls burial a bad idea for paper. A dry indoor spot — a cupboard, a loft, an interior wall cavity — is safer. If you do bury it, use dry ground, a second enclosure, a permanent marker and a written record of the position.

### What should you not put in a time capsule?

Food and anything organic, rubber, wool, untreated wood, newspaper clippings, adhesive tape, laminated items, batteries, and anything that needs a device to be read. In a sealed container, one item that breaks down damages the rest.

### Can I put photos and a USB drive in a time capsule?

Black-and-white prints last well; colour prints fade. Conservators advise against relying on digital media, because the hardware and software needed to read it may no longer exist. For video, sound and large numbers of photos, a digital time capsule that unlocks on a date is the better tool.

### How do I make sure my time capsule gets opened?

Tell several people, including someone younger than you; record the location and the opening date outside the capsule; register it with the International Time Capsule Society; and label the container with its opening date.