How archival are Fujifilm Instax prints, and how can I help them last longer?

There doesn’t seem to be clear published long-term archival data for Instax, so no firm lifespan can be stated from the information here. Based on general instant-film behavior, it’s safest to assume Instax is not especially archival compared with more stable print processes.

From the shared reports, Instax Monochrome should not be assumed to last longer than color; one cited source notes the monochrome material can shift toward sepia even if it doesn’t simply “fade” in the usual sense.

For longevity, use standard photo-preservation practices: keep prints cool, dry, and dark as much as possible. Heat, humidity, light, and frequent handling—especially in a kitchen—will all work against long-term stability. Since your prints will be unsleeved in a book that’s often handled, expect that environment to be less favorable than archival storage.

If these images are important family keepsakes, the practical takeaway is to reduce exposure to moisture, warmth, and light, and minimize direct handling where you can. Even if you keep using Instax for the look you want, storing the book in a stable, dry place when not in use will help prolong the images.