Let’s walk through the reasoning.

---

**1. Business profile**  
Italgas is a regulated gas distribution utility, with stable, predictable cash flows and long-life infrastructure assets. This makes it suitable for a higher level of debt, but also means it can attract senior debt at favorable rates without needing subordinated instruments.

**2. Current capital structure**  
From the balance sheet:

- Total assets (2023-01-01): ~€11,031m  
- Total equity (2023-01-01): ~€2,391m (equity ratio ~21.7%)  
- Current + non-current financial liabilities (excl. leases/other) are significant, and net debt is high.

This is already a leveraged balance sheet typical for utilities.

**3. Profit and coverage**  
- EBIT (2022/23): ~€641m  
- Finance costs: ~€61m  
- Interest cover is strong (over 10x EBIT/interest), which means there’s capacity for additional debt if needed.

**4. Hybrid bond rationale**  
Hybrids are used when:
- The company wants to maintain rating while leveraging further (equity credit from rating agencies).
- Tax efficiency (interest deductibility while preserving some equity characteristics).
- There is a need to finance growth without raising common equity.

For Italgas:
- Regulated returns mean limited upside, so the cost of hybrid coupons must be carefully weighed against allowed returns.
- It already has access to cheap senior debt; hybrids would be more expensive without a proportional benefit.
- No sign of distress or difficulty in raising senior debt.

**5. Market conditions**  
From the provided market data, interest rates have risen sharply in 2022 (swap rates above 1.7–1.9%), raising the absolute cost of all debt. Hybrids in euros for IG non-financials were yielding above 2.3% on average in 2022 (sub-sen delta ~0.2 over senior). This makes hybrid issuance relatively expensive.

**6. Conclusion**  
A small proportion of hybrids can optimize the WACC and maintain headroom within rating constraints, but given Italgas’s stable profile and high existing leverage, they would likely limit hybrid use to a modest share of the capital structure—around 25%—to keep financing costs down and preserve flexibility.

---

<answer>25%</answer>