From chat gpt:

Vaults are barrel-shaped cellular structures found in eukaryotic cells, and their exact function is still not fully understood. However, they are believed to play a role in several cellular processes, including:

1. Intracellular Transport – Vaults may help transport molecules, such as RNA and proteins, between different parts of the cell, including the nucleus and cytoplasm.

2. Detoxification – Some studies suggest that vaults help in detoxifying harmful substances, potentially by shuttling them out of the cell.

3. Drug Resistance – Vaults have been linked to multidrug resistance in cancer cells, possibly by expelling chemotherapy drugs from cells.

4. Immune Response – They may play a role in the immune system, though this is not yet well understood.

The "half-empty" appearance you mentioned comes from their hollow, cage-like structure, which allows them to encapsulate molecules.