A metal seed phrase backup is a copy of your recovery words stamped, punched, engraved or slotted into metal, usually stainless steel or titanium, so that it survives the fire, water and crushing that destroy paper. Both metals stay solid well above the temperature of a burning room, but design matters as much as material: in Jameson Lopp's independent stress tests of 75 devices, most failures came from aluminum parts, warped rails, dissolved rivets or markings that burned off. This guide compares the designs and metals, sums up the test results, and covers recording the words, passphrases and SLIP-39 shares, theft, a do-it-yourself option and a restore test. Where to keep the copies is covered in how to store a seed phrase.
Paper burns, and a flood can soak, smear or tear it. NIST's fire researchers put the temperature inside a room undergoing flashover, when everything in it ignites almost at once, at about 1,000 °C (1,832 °F). In Lopp's heat test, a card whose key was printed on paper glued to metal lost all of it.
Metal changes how a backup fails, not who can read it: a plate that survives a fire is just as readable to a burglar.
| Design | How it works | Pros | Cons |
|---|---|---|---|
| Stamped or engraved plate | Letters struck with letter stamps, or engraved, into a solid plate | One piece, no loose parts | Stamping is slow and easy to botch; shallow engraving can burn away |
| Center-punch grid plate | One dot per character in a grid of letters or digits | Fast and hard to get wrong | Unreadable without the grid, which must be etched deep |
| Letter tiles in a frame | Letter tiles slid into rails or slots | No stamping or punching; easy to fix mistakes | Up to 96 loose tiles; warped rails dropped tiles in tests |
| Washers on a bolt | One stamped word per washer side, stacked on a bolt under a cap nut | Hardware-store parts; cheap and private | Washers are awkward to stamp; each word needs its number |
| Capsule | Tiles threaded on a rod inside a screw-capped tube | Compact; acid did not reach the tiles in tests | A crushed tube can jam shut |
After testing dozens of devices, Lopp described the ideal in his treatise on seed backup design: stainless steel or titanium, small but thick (at least 5 mm, preferably over 1 cm), one solid piece, data center-punched or etched by electrolysis, and the decoding template etched into the device. Fasteners, he warns, can melt, dissolve in acid or seize up after crushing.
Alloys such as stainless steel and brass melt over a range rather than at one temperature. Figures come from the British Stainless Steel Association, PubChem's periodic table and the Copper Development Association:
| Material | Melting point or range | What it means for a backup |
|---|---|---|
| Stainless steel 304 | 1,400–1,450 °C (2,552–2,642 °F) | Solid well above room-fire temperatures |
| Stainless steel 316 / 316L | 1,375–1,400 °C (2,507–2,552 °F) | Resists salt better than 304; Lopp suggests 316L |
| Titanium (pure) | 1,668 °C (3,034 °F) | Lopp's other recommended metal |
| Copper (pure) | 1,085 °C (1,984 °F) | Just below Lopp's 1,093 °C test flame |
| Cartridge brass (70/30) | 916–954 °C (1,680–1,750 °F) | Melts below the ≈1,000 °C of a room in flashover |
| Aluminum (pure) | 660 °C (1,220 °F) | Melts far below that; Lopp's verdict is "a pile of slag" |
Melting point is only the first filter: several stainless steel devices failed the heat test without melting, because heat warped their rails and tiles fell out. With titanium, avoid steel fasteners, which Lopp says corrode galvanically against it.
Lopp's methodology applies three tests:
He calls the experiments not highly scientific and his grades arbitrary: A means he caused no data loss, F that the device was easy to destroy. Of the 75 devices in his results table, last updated in 2025, 45 earned an A in all three tests. Fourteen got an F in at least one test (10 for heat, 8 for corrosion and 5 for crushing), and six of those were too damaged by earlier tests to be crushed at all. His reviews show the patterns:
The grades apply to the versions he tested, and some products have since changed or been discontinued. His summary: more pieces mean more points of failure, and single plates with a grid for center-punched dots are the best value.
BIP39 built its English list so that the first four letters identify every word. All 2,048 words have a unique four-letter start, so a 24-word phrase fits in 96 letters.
Here is the public BIP39 test phrase, eleven times abandon and then about, in each form (never use it for funds):
Four letters: ABAN ABAN ABAN ABAN ABAN ABAN ABAN ABAN ABAN ABAN ABAN ABOU
Position 1-2048: 1 1 1 1 1 1 1 1 1 1 1 4
Index 0-2047: 0 0 0 0 0 0 0 0 0 0 0 3
The checksum catches most copying mistakes, not all: it has 4 bits in a 12-word phrase and 8 in a 24-word one, so roughly 1 in 16 or 1 in 256 wrong words still passes. If a letter later becomes unreadable, the other letters and the checksum usually narrow it down: see how to fix seed phrase errors.
Keep a BIP39 passphrase off the plate with the words: its point is that the words alone open a different wallet. Any passphrase opens a valid wallet, so a mistake shows no error, only an empty balance. Record it exactly, with capitals, digits, spaces and symbols, on a medium that can show every character; a plate made for seed words may offer only capital letters.
Each SLIP-39 share is a separate mnemonic that needs its own plate: 20 words for a 128-bit secret, 33 for a 256-bit one. Trezor's Safe 3 (since June 2024), Safe 5 and Safe 7 create a 20-word single-share backup by default. A 24-row plate holds a 20-word share but not a 33-word one. The SLIP-39 list has 1,024 words of 4 to 8 letters, each with a unique four-letter start, so four letters work here too, with three caveats:
See SLIP-39 vs BIP39 for the other differences.
Lopp's advice is to assume that anyone who gets hold of a backup can read it. Three ways to limit the damage:
Dots punched into a blank plate hide their meaning, but Lopp points out that this turns the backup into a 2-of-2 scheme: without the template, the plate is useless. Never accept a backup that arrives with words or keys already on it, or a seller's offer to engrave yours: whoever saw them can spend the funds, as in other seed phrase scams. Lopp also advises assuming that a vendor's shipping records will leak, and never having a device shipped to your home. For labels, tamper-evident bags and locations, see the storage guide above; for what your family needs to know, see crypto inheritance.
A hardware store has everything you need, and buying there leaves no order with a crypto vendor. The SAFU Ninja recipe Lopp tested uses three stainless steel parts: an M6 or 1/4-inch hex bolt 1 to 2 inches long, a matching acorn cap nut and M6 or 1/4 × 1-inch fender washers. It lost no data in any test, with an A for heat and acid and a B for crushing.
If stamping washers sounds too fiddly, Lopp finds a center punch on a plate with a deeply etched grid far easier than letter stamps. Two DIY plate projects he tested, with stamped and etched words, also got an A in every test.
A copy you have never restored from is unproven:
For the public test phrase, the first native SegWit address (m/84'/0'/0'/0/0) is the BIP84 test vector; with the passphrase TREZOR from the BIP39 test vectors, the same words open another wallet:
No passphrase: bc1qcr8te4kr609gcawutmrza0j4xv80jy8z306fyu
Passphrase TREZOR: bc1qv5rmq0kt9yz3pm36wvzct7p3x6mtgehjul0feu
Both are public test values, derived with the @scure libraries: never send funds to them, and never type your real words into a website or a "phrase checker."
Stainless steel and titanium melt well above the roughly 1,000 °C of a room in flashover. In Lopp's tests, 59 of 75 devices earned an A for heat after 10 minutes in a 1,093 °C flame; most of the 10 failures had aluminum parts or warping rails.
Both work. Titanium melts higher and 316L resists salt better than 304, but in the tests design mattered more than the metal.
Yes, for English BIP39 phrases and SLIP-39 shares, since both lists have unique four-letter starts. Leave three-letter words at three letters, and mark which standard the plate holds.
No. Keep it on a separate backup in a different place, recorded exactly, so that neither copy alone opens the wallet.