To determine the appropriate extent of hybrid bonds in the capital structure for HERA S.P.A., we must consider its financial profile as of the end of 2022.

1.  **Profitability and Interest Coverage:** HERA S.P.A. shows a stable operating performance, with "Profit Loss from Operating Activities" at 533.8 million EUR and "Profit Loss before Tax" at 408.8 million EUR. However, the company experienced a significant increase in "Finance Costs" from 300.3 million EUR (2021) to 217.2 million EUR (2022), reflecting shifts in the interest rate environment.
2.  **Debt and Leverage:** The company’s "Noncurrent Financial Liabilities" increased significantly from 3.71 billion EUR to 5.69 billion EUR between 2022 and 2023. With total liabilities rising to 13.47 billion EUR against equity of 3.64 billion EUR, the company is highly leveraged.
3.  **Market Environment:** The Swap Curves (5Y, 7Y, 10Y) show a dramatic increase in interest rates between 2021 and 2022 (e.g., 10Y swap rising from 0.053% to 1.927%). This rise in the cost of debt makes traditional borrowing more expensive.
4.  **Hybrid Bond Suitability:** Hybrid bonds (which provide equity-like credit treatment while maintaining debt status) are typically used by utilities or large industrial groups to optimize their capital structure and maintain credit ratings when debt loads are high. Given HERA's high leverage, its utility-like nature (stable cash flows), and the rising interest rate environment, maintaining a balanced approach is prudent. An allocation of 25% to hybrid instruments serves as an effective buffer to support credit ratings without overly diluting current shareholders or incurring the excessive costs of pure equity issuance. This moderate use of hybrids is standard for investment-grade utility companies managing heavy capital expenditure cycles and rising refinancing costs.

<answer>25%</answer>