Seed Phrase Storage: Metal Backups, Passphrases and Best Practices

Good seed phrase storage is the difference between holding bitcoin safely for decades and losing it in a single house fire. In Seed Phrases Explained you learned what a seed phrase is. Now you need to protect it. Your words are your bitcoin: if they’re destroyed, stolen or lost, the funds go with them. This lesson covers paper, metal, the optional passphrase, keeping copies in more than one place, and how to test your backup, ending with a checklist.

If you don’t have a hardware wallet yet, read this now for the ideas and come back to the checklist after you’ve set one up with How to Set Up a Hardware Wallet, with your words in front of you.

Why Seed Phrase Storage Matters

Self-custody means you are responsible for your backup. There’s no bank to call and no reset link. Your bitcoin is exactly as safe as your seed phrase backup.

Your backup has to survive:

• Fire. A fully developed house fire can exceed 600°C (1,100°F). Paper ignites at around 230°C (450°F).
• Water. Floods, burst pipes or a spilled drink can make ink run or smear.
• Time. Paper yellows, ink fades, pencil smudges.
• Theft. Anyone who finds your words can take your bitcoin in minutes, from anywhere.
• Loss. A house move, a forgotten hiding place, a relative throwing out “that piece of paper”.

No single method beats all five, but combining methods gets close.

Paper Backups: The Starting Point

Most backups start on paper: when your wallet shows the words, you write them down at once. A BitBox02 or BitBox02 Nova saves to its microSD card by default instead, but it can show the words later from its settings: write them down then.

How to Make a Paper Backup Correctly

1. Use the card that came with your hardware wallet. Most include numbered backup cards.
2. Write with a ballpoint pen, not pencil. Pencil smudges and fades; gel and felt-tip ink can run when wet.
3. Use block capitals, so similar letters can’t be confused.
4. Number every word: “1. ABANDON 2. ABILITY 3. ABLE…”. Order is part of the secret.
5. Check every word against the right word list. For a 12- or 24-word phrase, that’s the BIP39 list. A Trezor Safe’s default 20-word backup uses a different list (SLIP-39, 1,024 words): check it against Trezor’s list, not BIP39, or you may “correct” a word that was right.
6. Keep it somewhere secure and dry: a fire-resistant home safe, a locked cabinet or a bank safe deposit box.

Limitations of Paper

Paper is a starting point, not a permanent home: it burns well below house-fire temperatures, degrades with moisture, and ink fades over the years. If you’ll hold bitcoin for years, you need something more durable. That means metal.

Metal Seed Phrase Backups

A metal backup records your words on steel or titanium so they survive fire, water and time far better than paper.

Why Metal?

• Heat. Stainless steel (grades 304 and 316) melts at around 1,400°C and titanium at 1,668°C, far above a house fire. Melting point isn’t the whole story, though: in independent tests, some designs lose or shift their parts in heat or under crushing, so the device’s design matters as much as the metal.
• Water. Stainless steel and titanium don’t run or smudge, and resist corrosion.
• Time. Stamped or punched marks don’t fade.

Common Types

• Letter tiles: you slot individual letter tiles into a steel frame or tube (for example Cryptosteel Capsule, Billfodl). Compact, but assembly takes patience, and loose parts are a weak point.
• Punched plates: a steel plate printed with a grid of letters; you mark each letter with a centre punch and hammer (for example Blockplate, Coinkite’s SeedPlate). No loose parts.
• DIY washers: stainless steel washers from a hardware store, each word stamped with a letter-punch set and threaded onto a bolt in order. Cheap; how well it survives depends on the washers and how deep the stamping goes.

Metal Backup Comparison

Jameson Lopp, a Bitcoin security researcher, has stress-tested about 75 metal backup devices with heat, corrosion and crushing. His grades show how much design matters:

Product	Type	Material	Lopp stress-test grade (overall)	Ease of Use
Cryptosteel Capsule	Letter tiles	Stainless steel	A− (lower mark for crushing)	Moderate
Billfodl	Letter tiles	Stainless steel	C (weaker in heat and crushing)	Moderate
Blockplate	Centre-punched plate	Stainless steel	A	Easy
SeedPlate (Coinkite)	Centre-punched plate	Stainless steel	A	Easy
DIY washers	Letter stamps	Stainless steel	Not graded on that page	Moderate

Grades from Lopp’s metal storage reviews (checked November 2026), where you’ll also find current prices. His summary advice: simpler is better, because more pieces mean more ways to fail, and single plates with a punch grid are the best value. For product comparisons, see Cryptosteel vs. Billfodl and the Metal Seed Phrase Backup Complete Guide.

The BIP39 Passphrase (25th Word)

BIP39 includes an optional extra: a passphrase, sometimes called the “25th word”.

How It Works

When your words are turned into a seed (see Seed Phrases Explained), an optional passphrase is mixed in. A different passphrase, even one character different, produces a completely different wallet with different addresses and balances. No passphrase is itself a valid choice that opens one specific wallet. So the same 24 words with “alpha” and with “bravo” are two unrelated wallets.

Benefits

• Protection if your words are found. A thief with your words but not the passphrase can’t reach the funds behind it.
• A decoy option. You can keep a small amount in the wallet with no passphrase and your savings behind the real one. Under coercion you can reveal the words and the decoy (Course 5 covers physical security and coercion).
• No extra hardware. Most BIP39 wallets and hardware wallets support it.

Risks

• Forget the passphrase and the bitcoin is gone. It isn’t stored anywhere except where you put it.
• It needs its own backup, kept apart from the words. Storing them together defeats the purpose, so you now have two things to protect.
• Small typing differences matter. Capital letters, an extra space or a typo open a different, empty wallet.

The Decoy Wallet Strategy

1. Create a wallet with your words and no passphrase. Put a small amount in it (the decoy).
2. Add a passphrase to open a second wallet from the same words. This holds most of your bitcoin.
3. Store the words on metal and the passphrase written down, never in the same place (the multi-location plan below says how many copies of each).

If someone restores your words without the passphrase, they see only the decoy. Our 25th Word Guide covers setting it up.

Adding a Passphrase to Your Device

Each hardware wallet handles the passphrase in its own way, so follow your maker’s own guide, and type the passphrase on the device itself where it lets you. Then test it from paper, just as you test the words: open the passphrase wallet from your written copy, check that its first receiving address matches, and only then send funds to it. If you’re new to self-custody, wait: the setup in this course works without one, and a passphrase is worth adding once your words are safely stored and tested.

Multi-Location Storage Strategies

One backup in one place is one disaster away from total loss. Copies in separate places protect against a fire, flood or burglary at any one of them.

Don’t Split Your Seed Phrase

A common but dangerous idea is cutting the 24 words into pieces and keeping each piece somewhere different. It fails in one of two ways:

• Halves double the ways to lose it. With words 1–12 in one place and 13–24 in another, losing either place loses everything.
• “Two of three” splits weaken it. Cut the words into three groups of 8 and give each place two groups (16 words), so any two places can rebuild the seed. Whoever finds one place then has only 8 words to guess: about 2⁸⁰ combinations instead of 2²⁵⁶ (8 words carry 88 bits, minus the 8-bit checksum). For scale: 2⁸⁰ is about a trillion trillion. Bitcoin miners worldwide perform that many hashes roughly every 20 minutes (November 2026). Checking one seed guess costs far more work than one hash: each guess has to go through the 2,048 rounds of HMAC-SHA512 that BIP39 uses to turn words into a seed, and mining chips are built only for Bitcoin’s SHA-256 hash. So trying every combination is far beyond a thief’s computers today. Even so, the split has thrown away the safety margin your seed was designed around: NIST no longer counts 80 bits as adequate and allows nothing under 112 bits for protecting new data, and even a 12-word seed starts at 128. 2²⁵⁶ is beyond any computer. With a 12-word seed the same split leaves about 2⁴⁰, roughly what Coinkite estimated for the weakest Coldcard seeds of July 2026.

If you want your backup in pieces, use a scheme designed for it: SLIP-39 shares (below) or a multisig wallet with keys from different manufacturers (Course 5). Otherwise keep two or three complete copies in separate places. A passphrase kept apart from the words is another option, with its own cost: forget it and the funds are gone. Our seed split risk tool shows what a split does to the numbers.

Recommended Multi-Location Approach

1. Location A (home): a metal backup of the full seed in a fire-resistant safe.
2. Location B (off-site): a second metal or paper copy in a bank safe deposit box, or in a sealed, tamper-evident bag in a trusted relative’s safe.
3. Location C (optional): a third copy in another city or region, against regional disasters.
4. Passphrase (if used): two written copies, in two places that hold no copy of the words. With only one, a fire there locks you out of the funds behind it.

Shamir’s Secret Sharing (SLIP-39)

SLIP-39 splits a wallet’s secret into shares, for example 3-of-5: any 3 of the 5 rebuild it, and fewer than 3 reveal nothing about it. Unlike cutting up a word list, this is mathematically sound.

Trezor’s Multi-share Backup uses SLIP-39 on the Safe 3, Safe 5, Safe 7 and Model T, and Trezor lists Electrum, Sparrow, BlueWallet and Keystone among the other wallets that support it. SLIP-39 is a separate standard from BIP39. If your wallet was made with a BIP39 phrase, moving to shares means creating a new wallet and moving your funds to it. If your Trezor made a 20-word Single-share Backup, you’re already using SLIP-39, and Trezor can upgrade that backup to multiple shares; your original 20 words stay valid, so check the new shares before you decide what to do with the old copy. If you’re just starting out, two complete copies in separate places are simpler.

Testing Your Backup

A backup you haven’t tested is a backup you can’t trust. Test it before sending any significant amount to a new wallet.

How to Test Recovery

The test has to start from your written backup. Your device keeps its own copy of the seed, so anything it shows proves the device is right, not your paper. Several hardware wallets have a built-in check that erases nothing: Trezor’s Check backup and Ledger’s Recovery Check app have you type the words from your paper on the device and tell you whether they match. That is the safest first test. The full rehearsal goes like this:

1. Set up your wallet and write down the words.
2. Send a small test amount. A few thousand sats (satoshis, hundred-millionths of a bitcoin) is enough.
3. Restore on a second hardware wallet, or wipe your own. Wipe your only device only after the built-in check has passed and any passphrase has been tested, because a wrong paper would lock you out. Don’t use a phone or computer for this test: your words should never be typed into one.
4. Type the words from your written backup (and passphrase, if any) on the device. Read them from the paper, not from memory.
5. Check the balance and the first receiving address. They should match the original exactly. If they do, your backup works.
6. Then send larger amounts.

The test costs almost nothing and gives you real confidence. Repeat it after making a new metal copy, to make sure nothing was recorded wrongly. Each brand’s built-in check, including the Coldcard’s temporary-seed check, is listed step by step in How to Set Up a Hardware Wallet.

If your seed belongs to a phone wallet, keep only spending money there. Savings belong on a hardware wallet, where this test is safe. For a detailed walkthrough, including how to test a passphrase, see How to Test Your Seed Phrase Backup.

Seed Phrase Storage Best Practices Checklist

• ☐ Words written on paper as soon as your wallet shows them, not left to memory.
• ☐ At least one metal copy for fire and flood.
• ☐ Two or more complete copies in separate places.
• ☐ Every word numbered in every copy, and checked against the right word list.
• ☐ A note next to the words saying which wallet made them, which standard they use (BIP39 or SLIP-39) and the address type, so a future restore looks in the right place (Bitcoin Address Types and Derivation Paths). The passphrase stays off that note.
• ☐ Passphrase (if used) in two copies, stored apart from the words, never in the same place or container.
• ☐ No digital copies anywhere: no photos, cloud documents, text files, password managers or email drafts.
• ☐ Backup tested on a hardware wallet, never a phone or computer, starting with the built-in check.
• ☐ A trusted person knows the backup exists (not the words), so it can be found if something happens to you. That’s the first step of an inheritance plan; the rest, from written instructions to who gets which key, is taught in Course 5’s inheritance planning lesson.
• ☐ Locations protected: safes locked, bags sealed and tamper-evident.
• ☐ A yearly check of each backup’s physical condition.

If every box is ticked, your storage is solid. If you don’t have a hardware wallet yet, Hardware Wallets Explained is the place to start.

Frequently Asked Questions

What is the best material for a seed phrase backup?

Stainless steel (grade 304 or 316) or titanium. Both survive house fires, floods and corrosion; titanium is lighter and melts at a higher temperature, but stainless steel is enough for most people. Avoid aluminium: it melts at 660°C, too close to house-fire temperatures. And remember that the design matters too (see the table above).

Can I store my seed phrase in a password manager?

This course’s rule is no: keep your words only on paper or metal. A password manager is encrypted, but it lives on internet-connected devices and often in the cloud, so your words become reachable by malware on any of those devices, a breach of the provider, or anyone who gets your master password. That’s exactly the kind of remote theft a hardware wallet exists to prevent. Some experienced users accept that risk as an extra copy alongside their metal backup; if you’re learning, don’t.

How many copies of my seed phrase should I have?

Two or three. One copy is a single point of failure; more than three increases the chance someone finds one. Keep each in a different, secured place. A passphrase adds a second lock even if one copy is found.

What if I use a passphrase and forget it?

The bitcoin behind it is gone for good; there’s no recovery. Back the passphrase up as carefully as the words: at least two copies, in places that hold no copy of the words. The worst case is a strong passphrase that exists only in your memory and is then forgotten. More in the 25th word passphrase guide.

Is a bank safe deposit box a good place for a seed phrase backup?

It’s a reasonable off-site location with controlled access, with limits: access depends on opening hours and can be restricted in emergencies or legal disputes, authorities can open boxes with a warrant in some countries, and in many countries the contents aren’t insured by the bank. Use it as one location among several, and make sure someone you trust knows the box exists.

Five questions to check your seed

Most seeds are fine. These five questions find the few that are not. You can answer all of them without typing or showing your words anywhere.

1. Did a device with a known flaw make your seed? In July 2026 a Coldcard firmware flaw produced seeds that attackers could guess. Look up your device in our security advisories. If a Coldcard made your seed, use the two-minute Coldcard check.
2. Have you tested it, starting from the paper? A device showing the right address proves the device works, not your paper. The test means typing the words from your backup into a hardware wallet’s built-in check (for a small phone wallet with no hardware wallet, restoring them in the same app before you load money). How to test your backup.
3. If you use a passphrase, is it written down, and kept apart from the words? Without it, your words open a different, empty wallet. If it is forgotten, nobody can recover the funds.
4. Have you ever typed your words into a website or a form, or given them to someone in a chat who said they were “support”? No real company asks for them (how these scams work). If you have, treat the seed as exposed: move your funds to a new seed, made on a second device or following your maker’s guide, before you reset anything.
5. Do all your keys come from one manufacturer? Then one faulty generator can weaken all of them at once. Why three keys from one vendor are not multisig.

Go through it question by question with our seed backup checkup. It never asks for your words.

Print it for your family. This lesson is the basis of The Two-Envelope Plan, a printable kit your family can follow: two envelopes, a booklet for your heirs and two recovery runbooks.

Check Your Understanding

1. A friend suggests keeping words 1–12 at home and 13–24 at their house, “so nobody has the whole thing”. What’s wrong with that?

Answer

Losing either place loses the whole seed, so it doubles the ways to lose it. If you want pieces, use a scheme built for it (SLIP-39 shares or multisig); otherwise keep complete copies in separate places.

2. You’ve stamped your words on steel. Why is the job not finished?

Answer

You still have to test that the backup actually restores the wallet: type the words from the steel on your hardware wallet using its built-in check, and confirm they match. A copying mistake on metal is as fatal as one on paper.

3. Why is a passphrase both a protection and a risk?

Answer

It protects you because someone who finds your words can’t open the wallet behind the passphrase. It’s a risk because if you forget it, or lose its only copy, nobody can recover that wallet. So it needs its own backup, kept apart from the words.

Practical guides

• How to Test Your Seed Phrase Backup
• Metal Seed Phrase Backup: Complete Guide