Why Thermal Paper Destroys Seed Phrase Backups

In roughly one out of every five seed phrase audits we conduct, the client’s backup is written on thermal paper. Usually it is a receipt from a CU or GS25 convenience store, printed during a late-night wallet setup when proper stationery was not at hand.

Thermal paper works through a heat-sensitive coating. That coating continues to react with light, heat, and friction long after the receipt prints. Words that were crisp at setup become ghostly within two to four years. We have seen backups where only the indentation from a ballpoint pen remains — the ink itself has vanished entirely.

What to Use Instead

Archival-quality cotton paper, inscribed with a pigment-based pen (not gel ink, which can smear), stored flat in a paper envelope inside a fire-resistant container. Metal plates stamped with letter punches are durable but introduce their own risks: mis-stamped letters, difficulty reading under dim light, and the temptation to store the plate in the same location as the device it protects.

A Simple Test

Place your backup in a drawer for thirty days without looking at it. Then read each word aloud under normal room lighting without magnification. If any word requires squinting, it is time to re-inscribe before your next annual verification.