Mylar shelf-life calculator
“How long will it last?” has two answers, and people mix them up. The food sets the years; the mil thickness decides whether the bag survives long enough to deliver them. This tells you both.
Every estimate assumes the bag is packed with a correctly sized oxygen absorber, heat-sealed, and kept cool and dark. Heat is the single biggest life-shortener, a hot garage can halve these numbers.
The everyday long-term standard. The right thickness for most staples, a strong oxygen and light barrier that realises the full shelf life above when it's sealed well and kept cool.
Storing this inside a bucket or moving the bags around? Choose 7 mil for the extra puncture resistance.
Mil thickness is about durability, not a shelf-life dial
A common myth is that a thicker bag “lasts longer.” What actually stores your food for decades is removing the oxygen with an oxygen absorber. Mil thickness governs something different: how well the bag resists pinholes, punctures and light over time. A single pinhole lets oxygen back in and quietly undoes the whole seal, so the thickness you need is set by how the bag will be handled.
- 3.5 mil: short-to-medium term, gentle shelf storage. Not for buckets or bags that get moved.
- 5 mil: the everyday long-term standard, right for most staples.
- 7 mil: heavy-duty; the choice for bucket liners and rough handling, and the usual “25-year” benchmark bag.
Why some foods can't be saved by any bag
Low-moisture, low-oil staples (white rice, wheat, beans, oats, pasta) store for 25 to 30 years when oxygen is removed. But foods high in oil, like brown rice, nuts and whole-wheat flour, are limited by rancidity, not oxygen alone, and no barrier meaningfully extends them; expect one to two years and use the freezer for longer. The calculator flags these so a thick bag doesn't give you false confidence.
The one exception: sugar and salt
Sugar and salt keep almost indefinitely, but an oxygen absorber will fuse them into a solid block. Seal them dry in mylar on their own, no absorber. It's the one case where the usual advice is reversed.
Build the whole system
A bag is one piece. Pair the right mylar bags with a correctly sized oxygen absorber, and, for anything you'll stack or move, a food-grade bucket to protect the bags from pests and crushing.
Sources
- Utah State University Extension: dry-pack storage. Shelf-life ranges for dry staples stored with oxygen removed.
- LDS Home Storage Center: longer-term food supply. 30-year figures for low-moisture staples in oxygen-free packaging.
- TruePrepper: mylar mil thickness guide. How 3.5, 5 and 7 mil map to handling and use.