What to Put in a Time Capsule (and What Not To)

2026-10-26 · Yesterself

Most time capsule advice is a list of ideas. This is a list of survivors.

The difference matters, because a sealed container is not a neutral place. It is a small, still, unventilated room where whatever you put in acts on everything else for years without anyone watching. Half the disappointment people feel when a capsule is opened is not that the contents were boring. It is that something inside leaked, off-gassed, stuck, or bloomed, and took the good things with it.

So sort your contents twice. Once by what you want to say. Once by what will still be legible when the box is opened.

What survives well

These are the workhorses. If your capsule is mostly made of these, you are in good shape.

• Paper, printed or written with pigment. Plain uncoated paper, ideally cotton or acid-free, written with a pigment ink pen or printed on a laser printer. Toner is fused plastic and it stays put. Dye-based inkjet and gel pens fade far more readily, and ballpoint can spread.
• Photographic prints, loose. A real photographic print or a pigment print on cotton paper, in a plain paper envelope, will outlast almost anything else visual you own. Write on the back before it goes in.
• Cloth, natural and clean. A cotton patch, a linen handkerchief, a scrap of a shirt someone wore constantly. Wash it, dry it fully, and do not fold it around anything metal.
• Glass, glazed ceramic, stainless steel. Marbles, a small tile, a key, a coin, a pin. Inert, stable, and pleasant to hold in twelve years.
• Anything printed you did not choose deliberately. A ticket stub, a receipt on ordinary paper, a printed schedule, a takeout menu. Ephemera is the strongest form of evidence in a capsule, because nobody was performing when they made it.

Objects survive better than they signify. A good rule: for every object, add a card.

What to write, since writing is the part that carries

Objects age well and explain badly. Text is the opposite of a mystery, and it is also the cheapest and lightest thing you can include, so include more of it than feels reasonable.

Worth writing down:

1. A plain day. Not a summary of the year. One ordinary Tuesday, hour by hour, including what things cost and what you ate and what annoyed you. This is the page people reread.
2. Open questions. Things you genuinely do not know the answer to yet. Whether the move works out. Whether the friendship holds. A capsule that asks questions is far more interesting to open than one that makes announcements.
3. A list of names. Everyone who was regularly in your life at that moment, with one line each. Memory drops names faster than it drops feelings.
4. What you assume is permanent. The apps you use daily, the road you drive, the price of a coffee, the job you think you will still have. Nothing dates so vividly as a confident assumption.
5. An index. One page listing every item in the box and why it is there. This single page does more work than any object in it.

If you want more on the writing side, letter to your future self examples covers the letter itself, and how to make a time capsule covers the container and the sealing.

The exclusion list

This is the part usually left out. These items do not merely fail; they damage their neighbors.

• Batteries. Any battery left in any device. Alkaline cells leak a caustic residue that eats contacts and turns nearby paper brittle and stained. Lithium cells can fail worse. Remove every one, including the button cell in the watch or the toy. If the device matters, put it in with a note saying which battery it took.
• Thermal paper receipts. The glossy slips from card terminals and gas pumps. The image is heat-developed dye, and it fades to a blank gray slip on its own, faster in warmth. If a receipt matters, photocopy it or write out what it said and include that instead.
• Rubber bands, foam, and soft plastics. Rubber perishes into a sticky tar that bonds permanently to paper and cloth. Old foam crumbles into dust that gets everywhere. Cheap soft PVC weeps a plasticizer film onto whatever it touches.
• Anything on adhesive tape. Tape yellows, the carrier separates from the glue, and the glue soaks into paper and stains it in a hard brown line. This includes sticky notes, tape used to fix a photo to a page, and label stickers. Use a paper clip cut from stainless steel, a slipped folder, or nothing at all.
• Food, seeds, and anything organic. Candy, gum, a tea bag, dried flowers, a pressed leaf, a lock of hair with skin on it. These attract pests, hold moisture, and mold. A capsule that grows mold loses everything paper inside it.
• Photographs sealed in plastic. Magnetic albums, laminating pouches, PVC sleeves, and cling wrap all bond to emulsion over time. Laminate is permanent and irreversible. Loose in paper is better than protected in plastic.
• Newspaper, if it touches anything. Newsprint is highly acidic and it transfers that acid to whatever it sits against. You can include a clipping, but isolate it in its own envelope.
• Liquids, aerosols, and anything pressurized. A perfume sample, a lighter, a small bottle. They leak.
• Coins and keys resting on paper. Metal in contact with paper leaves an oxide stain shaped like the object. Bag them separately in paper, not in plastic.

The two questions that settle most edge cases

When you are holding something and cannot decide, ask:

Will it change on its own? Rubber, tape, thermal paper, food, and batteries all have a chemistry running quietly inside them. Glass, cotton, ceramic, and toner do not, to any practical degree.

If it fails, does it fail alone? A dead USB drive is a mild loss. A leaked battery is a catastrophic one, because it takes the letters with it. Anything that fails messily should either be excluded or isolated in its own sealed paper envelope at the edge of the box.

Digital items sit awkwardly across both questions. A drive can survive physically and still be unreadable because nothing left will accept the connector or the file format. If you include one, treat it as a supplement and print an index of what it holds. Digital versus physical time capsule goes further into that trade.

A note on the writing that does not go in the box

The strongest thing in most capsules is the paper, and paper does not have to wait in a container to reach you. Some people keep the physical box for objects and let the words travel separately, arriving on a chosen date rather than at an excavation.

That is the shape of Yesterself, a journaling app for iOS and Android built on one loop: each morning it brings you a letter drawn from your own past writing, and your reply that evening becomes tomorrow's mail. Any sentence can be postmarked to a future date and will arrive on that day. It is end-to-end encrypted, with no account, no email, and no password; your identity is twelve words you hold, the server stores ciphertext it cannot read, and export is free forever in open formats. It is not released yet, so the only thing to do today is join the waiting list on the site.

Before you seal it

Lay everything out on a table first. Walk the exclusion list item by item, out loud if it helps. Pull the batteries. Photocopy the thermal receipts. Take the tape off. Put the coins in their own envelope.

Then add the index card you almost certainly have not written, the one that says what the box is, who made it, on what date, and when it is meant to be opened. Tape nothing. Write the date on the outside in pigment ink.

The capsule is not really a container of objects. It is a letter with exhibits attached, and the exhibits are the part most likely to spoil the letter. Choose them like a person who has seen a box opened badly.

Common questions

What lasts longest in a time capsule?

Paper printed with pigment ink, cotton or linen cloth, glazed ceramic, glass, and stainless steel are the most durable common items. They change slowly and they do not attack the things stored next to them.

Can I put photographs in a time capsule?

Yes, if they are true photographic prints or pigment prints on cotton paper, kept loose in a paper envelope. Do not seal them inside plastic sleeves, magnetic albums, or laminate.

Why are batteries a problem in a time capsule?

Cells left in a device for years can leak an alkaline or acidic residue that corrodes metal contacts and destroys the paper around them. Take every battery out and store it somewhere else.

Should I include a USB drive?

You can, but treat it as a bonus rather than the record. Add a printed page listing what is on it and which formats it uses, so the contents are still knowable if the drive fails.

How much should I write to go with the objects?

More than feels necessary. An object with no note attached becomes a puzzle. One index card per item, saying what it is and why it mattered, is usually enough.