The case for metal is one number. Paper ignites somewhere around 233 °C. A house fire commonly runs 600–1,000 °C. Stainless steel melts near 1,425 °C. Everything else about metal backups is detail; that gap is the argument.
This page is about the medium itself — which formats survive, what to look for, and where people go wrong. Where to keep the backup is a separate question and arguably the more important one.
We do not make or sell backup plates or anything else. Some links earn a commission; it does not change what is written here, including the section on making your own for a few pounds.
What actually kills a paper backup
Fire is the dramatic one, and it is not the most common. In rough order of how often each occurs:
- Fading. Ballpoint and gel inks fade with light and age. Thermal receipt paper goes blank on its own within a few years, faster in warmth.
- Water. A burst pipe, a damp cellar, a leaking roof. Ink runs; paper pulps.
- Handling. Folding, creasing, smudged pencil, coffee.
- Being thrown away. An unlabelled scrap of paper looks exactly like rubbish to anyone tidying.
- Fire. Rare, total, and the one metal is explicitly designed for.
Metal solves all five except the last. Nothing solves “thrown away” except telling somebody the backup exists.
The four formats
Stamped plates. You hammer hardened letter punches into a steel plate. Slow — expect an hour for 24 words — permanent, cheap, and effectively indestructible. The marks are deep enough to survive a fire that warps the plate. This is the most durable option and the least forgiving of mistakes, since there is no undo.
Tile and washer systems. Pre-engraved letter tiles slot into a rail or stack onto a bolt. Fast to assemble, reusable, and legible. The weakness is mechanical: if the housing fails or you drop an unsecured stack, you have the right letters in the wrong order — and order is part of the secret. Anything using this design needs its closure checked and, ideally, tamper-evident.
Engraved or etched cards. Fast with a rotary tool. The catch is depth: a shallow scratch can be polished off by abrasion, and heat plus oxidation can make faint marks hard to read. Acceptable if you engrave deeply; poor if you are tracing.
Punched-hole grids. A plate printed with a letter matrix where you punch out the correct cells. Fast and very durable, but the encoding is opaque — someone recovering it later must work out how to read it, which makes it a poor choice for inheritance unless you leave instructions.
What to look for
- Stainless steel, 304 or 316. Both handle fire and corrosion well; 316 resists salt air better, which matters near the coast. Avoid aluminium — it melts around 660 °C, inside the range a house fire reaches.
- Thickness. Thin plates warp; thicker stock holds its shape and its marks.
- Only four letters per word. Every BIP-39 word is uniquely identified by its first four letters, so kits give you four columns. This is a property of the standard, not a shortcut.
- Room for 24 words, even if you have 12 today.
- A closure that cannot open in a fall, for tile systems.
- Numbered rows. Order is part of the secret and unnumbered rows lose it.
Making your own
A letter punch set and a strip of stainless steel from a hardware shop will cost a fraction of a branded kit and perform just as well. The physics does not care about the logo.
Two cautions. Practise on scrap first — punch alignment is harder than it looks and the first attempt is usually crooked enough to be ambiguous later. And do the work somewhere private: this is the one moment your entire phrase is laid out in the open, which is precisely when a window, a doorbell camera or a laptop webcam becomes a problem.
The mistakes
- Stamping straight from the device screen. Write on paper first, verify it word by word, then transfer to metal. Stamping errors cannot be corrected.
- Not numbering the rows. Correct words in unknown order is a failed backup.
- Engraving the passphrase on the same plate. That collapses two independent secrets into one object and defeats the point of having a passphrase at all.
- Labelling it. “BTC seed” engraved on the plate turns a piece of anonymous metal into a signpost.
- Treating metal as a substitute for a second copy. A single indestructible backup in one building is still a single point of failure — it can be stolen, or the building can become inaccessible.
- Never verifying it. The whole point is a backup that works decades from now. Test it before you rely on it.
Is it worth it?
If you hold a small amount and would not be badly hurt losing it, a carefully written paper backup in two dry locations is a reasonable place to stop. Metal is not magic; it addresses one failure mode very well.
It becomes clearly worth it when the amount at stake exceeds the cost by a wide margin, when the holding is long-term, or when a backup needs to remain readable by someone else years from now. That last case is inheritance, and it is where durability stops being about fire and starts being about time.