Ash doesn't decompose. Once cremation is done, what's left is inert bone fragment: no bacteria, no organic matter, nothing left to break down.

Ashes inside a cremation urn will actually outlast the urn itself, not the other way round.

The real question is whether the urn holds up. Solid brass and rosewood age well; thin aluminium or resin can crack, discolour, or lose its seal after a decade in sunlight or a humid room.

A loose lid isn't just cosmetic. It's how moisture gets in.

If you're choosing a cremation urn to keep for good, material and seal quality matter more than anything else on the spec sheet. Ashes will keep. Whether the urn protects them comes down to what it's made from.

Most people start their search at a funeral home, then realise the range is thin, just a handful of styles at a fixed markup.

Pure Memorials runs one of the larger online catalogues of urns for ashes in NZ, covering brass and aluminium cremation urns through to carved wooden pieces and small keepsake urns.

Buying online also makes the process easier. You're not being shown three options in a showroom while someone waits on you.

You can sit with it, compare finishes, and decide when you're ready. Shipping covers the country, tracked and properly packaged.

Full adult cremation urn, a keepsake to split between family, or something for a pet, it's a decision that's easier to make without a countdown clock running.

There's a rough formula funeral suppliers use: about one cubic inch of urn space per pound the person weighed.

Work that out for a typical adult and you land somewhere between 180 and 220 cubic inches, which is what most standard cremation urns are built around.

Heavier build? Size up. Plenty of suppliers stock extra-large urns for ashes at 300 cubic inches or more, and going bigger is always the safer call.

Keepsake urns sit outside this whole equation. They're built to hold a token amount, not the full remains.

Check the listed capacity before buying rather than assuming it'll fit. It's the one spec on a cremation urn that genuinely has a wrong answer if you get it wrong.

A full-size cremation urn is built for one job: holding everything, typically 180 to 220 cubic inches for an adult.

A keepsake urn holds almost nothing by comparison, just a few cubic inches, enough for a token amount.

Why would anyone want less capacity? Usually it's about splitting ashes between family members, or wanting something small and personal while the rest stays in the main urn or gets scattered.

Neither one is the correct choice, they're just built for different situations.

If your family's all in one place, a single urn for ashes probably covers it. If people are spread out and each want to hold onto something, a few keepsake urns alongside the main one tends to work better.