Physical storage: paper, metal & places

Your backup must outlive fire, flood, damp, curious relatives, burglars and decades of neglect, and still be readable by you and your heirs. This page sets out the evidence on what survives, where to keep it, and how to combine physical backups with passphrases, SLIP-39 and multisig. It is educational information, not advice.

At a glance: physical storage in six points Beginner

1. Paper is a starting point, not a destination. It burns, soaks and fades. Fine for a first copy while you set things up; move to metal for meaningful sums.
2. Choose stainless steel or titanium, with the characters punched or stamped in. In independent tests, simple one-piece plates did best; loose-tile designs failed more often (evidence).
3. Avoid aluminium, brass, copper and zinc for the part that carries your words. Their melting points are at or below the temperatures reached in house fires and in test torches (table).
4. Metal does not stop thieves. Anyone who finds a plain seed backup can take your funds. Hiding it well, sealing it in a tamper-evident bag, and (for larger sums) a passphrase, SLIP-39 or multisig deal with that.
5. Two copies, two places. One fire, flood or burglary should not wipe out every copy. But each extra copy is another thing to steal, which is why splitting schemes exist (location strategy).
6. Check it, then check it again. Verify each copy with your wallet's "check backup" feature before you rely on it, and look at stored copies on a schedule (maintenance). Make sure someone you trust will be able to find and use it (estate planning).

What can destroy a backup?

Melting-point note: aluminium (about 660 °C) and brass (about 916–954 °C) can fail in house fires; prefer stainless steel or titanium. Figures and sources are in the materials table.

Threat matrix: what protects against what Intermediate

No single choice covers every threat. Material choice deals with the physical threats at the top; location and design deal with people. "Design" means how the secret is split, for example a passphrase, SLIP-39 shares or multisig.

Sources: stress-test results from Lopp's metal storage reviews; post-fire retrieval risks from Lopp's How to Back Up a Seed Phrase; institutional risks in safe deposit boxes below.

Materials compared Beginner Intermediate

Melting point is not the only thing that matters. Corrosion, how deep the characters go, and how many separate parts can fall apart matter as much. Melting points are rounded; alloys melt over a range.

Sources: stainless grades, titanium grades, galling and galvanic corrosion from Lopp's Treatise on Bitcoin Seed Backup Device Design (2022); element melting points from the Royal Society of Chemistry: titanium 1,670 °C, copper 1,084.62 °C, aluminium 660.32 °C, zinc 419.53 °C; cartridge brass C26000 solidus 916 °C, liquidus 954 °C (AZoM); grades from Lopp's table, including the Copper Seed Safe and Keyois Capsule reviews.

Formats compared

Paper, lamination and stone paper Beginner

On lamination: the University of Illinois Preservation Self-Assessment Program describes heat-seal lamination as irreversible, and says laminate plastics can "off-gas" and their adhesives can make inks bleed (PSAP). If you want a paper copy kept dry, a resealable plastic bag (as the FDIC suggests for safe-deposit contents) can be opened and checked; lamination cannot.

Metal backups: types and test evidence Beginner

Independent stress tests by Bitcoin security engineer Jameson Lopp — propane torch (1,093 °C), acid bath, and a 20-ton hydraulic press — have covered 75 devices. His published conclusion: simple single plates with centre-punched or stamped characters are generally the best value; multi-part tile designs have more ways to fail (reviews, round III write-up).

*Grades from Lopp's public table (checked October 2026). Products are redesigned; tested units may differ from current ones. Verify before buying.

Stress-test evidence: fire, acid and crush Intermediate

The most widely cited public dataset is Jameson Lopp's Metal Bitcoin Seed Storage Reviews, covering 75 devices. His method:

• Heat: a large propane torch giving a 1,093 °C (2,000 °F) flame over 4 inches (about 10 cm) across, checked with a thermometer, for 10 minutes or until failure. Then a plunge into a bucket of water, to simulate firefighters putting the fire out. He notes that failures usually happened around the 5-minute mark.
• Corrosion: 12 hours in 16% muriatic (hydrochloric) acid, or until bubbling stops. He says this is deliberately more extreme than most people will face.
• Crush: a 20-ton hydraulic press, then a check that the data can still be read.
• Grading: A means he could not cause data loss; F means it was easy to destroy. He calls the grading "arbitrary" and the tests "not highly scientific": they rank devices against each other.

Grades copied from Lopp's public table and the linked individual reviews, checked 24 October 2026. Lopp says he will not test many more devices because most new products resemble ones already tested. Products are redesigned, so a tested unit may differ from what is sold today.

What the tests say makes a good device Intermediate

From Lopp's design treatise, written after stress-testing about 70 devices:

• Stainless steel or titanium, ideally 316L stainless steel or grade 4 or 7 titanium. "Don't cheap out and use aluminum unless you want a pile of slag."
• Small but thick. He suggests at least 5 mm of metal, preferably over 1 cm. Long, thin plates flex; large stacks hold heat and can deform when hosed with water.
• One solid piece, with as few fasteners as possible. He has seen fasteners melt, dissolve in acid, strip, or seize a crushed device shut.
• Centre-punched or electrolysis-etched data. He found stamping "arduous" (missed strikes, double strikes, rotated letters), and a light centre-punch strike is easy to redo.
• The decoding template etched as deeply as the data. Printed or lightly etched templates were erased by heat or acid, leaving dots with no meaning.
• Words, not numbers, where space allows. If one character becomes unreadable, four stored letters usually leave about 2 possible words; a stored word number can leave up to 10.
• If you use tiles, one tile per word, numbered. If 96 single-letter tiles get mixed up, there are 96! (about 10¹⁵⁰) possible orders.
• Privacy: assume a seller's shipping list will leak. Do not have backup products delivered to the place where you will keep them; hardware-shop DIY avoids the issue.

DIY metal backup — step by step Intermediate

1. Buy 304 or 316 stainless washers (e.g. M10, 2–3 mm thick) or a plain plate, a 3 mm letter/number punch set and a hammer from a hardware shop. Pay cash if privacy matters.
2. Practise on scrap: strike firmly once, on a solid steel or concrete surface.
3. Stamp the word number and the first four letters (e.g. "01 WORD" format), one word per washer or per line.
4. Assemble washers on a stainless bolt with a locking nut; optionally secure with a tamper-evident sealed bag.
5. Verify against the device; then destroy any scrap pieces that contain real letters.

Lopp's reviews give A grades to DIY designs such as Steel Wallet (DIY) and Bulletproof Bitcoin (DIY). If you buy a kit, makers such as Trezor advise marking the letters first, checking the marked letters with the device's Check backup feature, and only then punching (Trezor Keep Metal guide). That is good practice for any metal backup.

How hot is a house fire? Intermediate

• How common: fire and rescue services in England attended 26,180 dwelling fires in the year to March 2026 (Home Office statistics). The US Fire Administration estimates 344,600 residential building fires in the US in 2023 (USFA).
• How hot: a NIST fact sheet for firefighters gives over 400 °C for gases at the start of room flashover, and about 1,000 °C inside a room undergoing flashover (NIST SP 1102). Lopp's site puts typical house-fire peaks at around 704 °C (why stress test). Temperatures vary greatly with fuel, ventilation and duration, so plan for the higher figure.
• What that means: paper and plastics burn; aluminium (660 °C) and zinc (420 °C) melt; brass and copper are close to their melting range at the top end. Stainless steel and titanium melt well above these temperatures. Lopp's 1,093 °C torch is a little hotter than the NIST flashover figure.
• Surviving is not the same as getting it back. Lopp lists ways a backup that survives can still be lost: fire hoses washing it into run-off, someone sifting the rubble pocketing it, or the site being condemned so only hazmat crews may enter (How to Back Up a Seed Phrase). That is the case for a second location.

Fire safes and what their ratings mean Intermediate

Fire ratings test whether a container keeps its inside cool enough for paper or media for a set time. They do not test whether it stops a burglar, and they do not test immersion in water.

Sources: UL 72 scope (UL Standards & Engagement); American Security: fire ratings explained and KL Security: UL fire rating (manufacturer and dealer summaries of the UL test); BSI Knowledge on BS EN 15659 and BS EN 1047-1; An Garda Síochána: secure safes and standards.

SeedQR and CompactSeedQR Intermediate

Developed by the SeedSigner project (specification). Your BIP39 words are encoded as word-index digits (Standard SeedQR) or raw entropy bits (CompactSeedQR) and drawn by hand onto a printed grid (21×21 or 25×25 for 12 words; 25×25 or 29×29 for 24), or punched onto steel.

Encoding tricks (not encryption) Intermediate

• First four letters: enough to identify any English BIP39 word — saves space on metal.
• Word index numbers (1–2048): compact; looks like "just numbers" but is trivially decoded by anyone who knows BIP39.
• Binary/hex of the entropy: compact but error-prone.

Obfuscation and steganography — caveats Expert

People hide words in books, change word order with a "secret rule", add fake words, or shift indices by a memorised number. Community consensus is cautious:

Where to keep backups Intermediate

Use tamper-evident bags (numbered security bags) around off-site backups and record the serial numbers: on each check you can tell whether anyone opened it.

Safe deposit boxes in the UK and US Intermediate

United Kingdom: a shrinking service

• Most high-street banks have closed their services. Barclays has closed Barclaysafe and is returning stored items (Barclays). NatWest and RBS say they have "made the difficult decision" to close Safe Custody (NatWest, RBS). Bank of Scotland closed Safe Custody to new items in 2001 and points customers to a Lloyds safe deposit box product (Bank of Scotland). In 2016 the Sunday Times reported that HSBC was phasing out closed safe keeping, with 30 days' notice to collect items (The Times).
• Some providers remain. Metro Bank offers boxes in most of its stores to customers who hold a Metro Bank account. Its published prices in October 2026 ran from £255 a year (extra small) to £801 a year (extra large), and it suggests insuring the contents yourself (Metro Bank). Prices and availability change; check directly.
• On death: Bank of Scotland, for example, returns Safe Custody items to the executor and needs a grant of probate if the items are valuable. Expect a delay before anyone can reach a box after a death. See the UK estate guide.

United States: not insured, and state law decides access

• Not FDIC-insured. The FDIC says a safe deposit box "is not a deposit account", so its contents are not covered by deposit insurance, and banks generally do not insure contents either. It suggests asking your home or renter's insurer about cover (FDIC).
• Access on death depends on state law, which "restrict[s] entry … to certain individuals" under controlled conditions (FDIC). Joint renters get unrestricted access, and the bank is unlikely to be responsible for what they remove.
• Unpaid boxes can pass to the state. If fees go unpaid, a box is typically treated as dormant after three to five years (set by state statute). Its contents may then be sent to the state's unclaimed-property office, a process called escheat (OCC HelpWithMyBank, NAUPA). A metal plate with words on it may mean nothing to the person cataloguing it.
• Private vaults carry their own risks. In 2021 the FBI seized boxes at US Private Vaults in Beverly Hills while investigating the business. In January 2024 the Ninth Circuit held that the FBI's "inventory" of about 700 boxes exceeded the warrant and violated the Fourth Amendment (Snitko v. United States). Box holders' property was caught up in an investigation of someone else.

Location strategy and geographic separation Intermediate

Lopp's rule of thumb: if any single location holds enough to steal the funds, it is a single point of failure, and no single disaster should be able to destroy copies in several places at once. But don't spread things so widely that you never check them. A patient attacker could compromise backups one by one over years (Lopp).

The layouts follow from how each scheme works. See SLIP-39 vs multisig and the expert section below.

Choosing sites

• Different risks, not just different addresses. Two houses on the same flood plain, or the same street in a wildfire area, share a disaster.
• Reachable within a day or two. You need to check them, and your heirs need to collect them.
• People you trust, holding only a part. A relative or friend can hold one share or one multisig key, sealed and labelled "do not open, contact X". Never a whole single-sig seed.
• Professionals for documents, not secrets. A solicitor or attorney can hold your will and letter of instruction; see custody & services.
• Privacy. Don't tell people how much you hold or what the sealed packet is; avoid deliveries of backup products to the storage address.

Checking and maintaining stored backups Intermediate

1. Day one: verify each copy with your wallet's built-in check (for example "Check backup" on Trezor, or a dry-run recovery on devices that offer one), reading from the stored copy, not from your notes.
2. Seal and log: put each copy in a numbered tamper-evident bag. Photograph the outside of the sealed bag only and record the serial number in your inventory. Lopp suggests signing the bag too.
3. Yearly: inspect each bag for tampering. Check paper copies for fading or damp, and metal for corrosion. Make sure each location still exists and is still accessible.
4. After any event (burglary, flood, a move, a relationship ending, a bank closing its box service): treat the affected copy as possibly compromised. If a whole secret might have been seen, move the funds to a new wallet.
5. Every few years: do a full test restore with a small amount, update your letter of instruction, and confirm the wallet software can still read your format.

Pros, cons, pitfalls and community advice: summary Beginner Intermediate

Expert: combining metal with passphrases, SLIP-39 and multisig Expert

Physical storage and secret-splitting solve different problems. Metal protects against destruction; splitting protects against discovery. The art is to get both without creating a scheme you or your heirs cannot operate.

BIP39 passphrase

• A passphrase makes a found seed plate useless on its own. Lopp warns that this is effectively a 2-of-2 arrangement with two single points of failure, and that he has seen many people locked out by a lost passphrase (Lopp).
• So the passphrase needs its own durable, redundant backup, never stored with the seed. As the layout table shows, that means four items across four sites to survive the loss of any one site without ever keeping the seed and passphrase together.
• Stamp the passphrase exactly, including capitals, spaces and symbols. Some makers sell separate passphrase plates (Lopp graded the Coldbit Passphrase plate A−).

SLIP-39 (Shamir) shares

• Each share is a separate 20-word list. Trezor's Keep Metal Multi-share has a section to record the total number of shares and the threshold, and each share needs its own capsule (Trezor, setup guide).
• A 2-of-3 layout puts one share plate in each of three sites. Losing one site loses nothing; finding one share reveals nothing useful (per the SLIP-39 specification).
• Record the scheme on every plate ("share 2 of 3, threshold 2") and write down which wallets can restore SLIP-39. BIP39-only wallets cannot (see SLIP-39).

Multisig

• Back up each key's seed on metal and store them in different sites. Also keep a copy of the wallet descriptor (or the xpubs, derivation paths and threshold) with every seed backup. Lopp suggests keeping it inside the same tamper-evident bag: it cannot spend funds on its own, but without it recovery can become a "treasure hunt" (Lopp). The descriptor does reveal your balances and history, so treat it as private.
• Consider different metal products or formats for different keys, so that one design flaw cannot affect every copy.
• See multisig and the 10x Security Bitcoin Guide.

Seed XOR and other N-of-N splits

Seed XOR splits a seed into parts that are each valid-looking seeds, but you need all of them. Lopp notes you will want multiple sets so that losing one plate is not catastrophic (Lopp, seedxor.com). See Seed XOR.

Real-world incidents Intermediate

These are sourced reports relevant to physical storage. More are in the case files. We found no published, independently verified case of a correctly made A-grade metal backup being destroyed by a house fire, and none is claimed here.

Physical storage checklist Beginner

• Metal copy made from stainless steel or titanium, with punched or stamped characters
• Each copy verified with the device, reading from the stored copy
• At least two copies in places that don't share a fire, flood or burglar, or a splitting scheme
• No single location holds enough to steal the funds (for larger sums)
• Passphrase, if used, backed up as durably as the seed, and never stored with it
• Wallet details (type, derivation path, descriptor) recorded alongside
• Tamper-evident bags; serial numbers logged
• Bank or vault box fees paid; box recorded for your executor
• A yearly inspection date in your calendar
• Letter of instruction updated, explaining where things are, without any secrets

Printable versions: backup checklist and inventory template.

Last reviewed: 23 October 2026 · Educational information only — verify current details with official sources.