Fortum’s financial profile in 2022 shows a substantial reduction in both assets and equity, reflecting the divestment of large parts of the business. Net debt, approximated from reported financial liabilities, is roughly €7.8 bn, while comparable EBITDA is €2.4 bn, giving a net‑debt‑to‑EBITDA ratio of about 3.2× – a level that is acceptable for an investment‑grade utility but leaves limited headroom for additional leverage. Interest coverage (EBITDA/interest expense) is comfortable at around 13×, indicating that the company can service debt without difficulty, but any new debt will increase this burden.

Hybrid bonds are attractive because rating agencies treat them as 50 % equity, which improves reported leverage metrics (e.g., FFO/Debt) and can support the current credit rating. At the same time, the current market environment shows relatively high nominal rates: the 5‑year and 10‑year swap averages are around 1.7–1.9 % in 2022, and the sub‑senior segment of the iBoxx EUR Non‑Financial IG index yields roughly 2.3 % on average. Hybrid issuance therefore carries a cost that, while lower than pure equity, is still meaningful and will erode coverage if used excessively.

Given Fortum’s moderate leverage, strong interest coverage, and the strategic benefit of maintaining equity credit for rating purposes, a modest reliance on hybrid financing is appropriate. An allocation of roughly one‑quarter of total debt (≈ 25 % of the capital structure) balances the cost advantage of hybrids with the need to preserve financial flexibility and avoid over‑reliance on more expensive hybrid instruments in a high‑rate environment.

<answer>25%</answer>