### Which Type of Batch to Use

Immutable batches are suitable for long term storage of data or for data which otherwise does not need to be changed and should never be overwritten, such as records archival, legal documents, family photos, etc.

Mutable batches are great for data which needs to be frequently updated and does not require a guarantee of immutability. For example, a blog, personal or company websites, ephemeral messaging app, etc.

The default batch type when unspecified is immutable. This can be modified through the Bee api by setting the `immutable` header with the [`\stamps POST` endpoint](https://docs.ethswarm.org/api/#tag/Transaction/paths/~1transactions~1%7BtxHash%7D/post) to `false`.

### Implications for Swarm Users

Due to the nature of batch utilisation described above, batches are often fully utilised before reaching their theoretical maximum storage amount. However as the batch depth increases, the chance of a postage batch becoming fully utilised early decreases. At at batch depth 23, it is statistically highly unlikely that the batch will be fully utilised/start replacing old chunks before reaching 50% of its theoretical maximum. Therefore, when choosing a batch depth, it is recommended to use a batch depth of 23 or greater, and consider 50% of its theoretical maximum storage amount as the de facto maximum storage amount.

Let's look at an example to make it clearer. Using the method of calculating the theoretical maximum storage amount [outlined above](/docs/learn/technology/contracts/postage-stamp#batch-depth), we can see that for a batch depth of 23, the maximum amount which can be stored is 33,554,432 kb:

$$
2^{23} \times \text{4kb} = \text{33,554,432 kb}
$$

Therefore we should use 50% of that value as our de facto storage limit:

$$
\text{33,554,432 kb} \times{0.5} = \text{16,777,216 kb}
$$

We find that at depth 23, we have a statistical guarantee of being able to store up to 16,777,216 kb or 16.77 gb worth of data.

:::info
More information about the expected utilisation levels for different batch depths will be added in the near future.
:::