To determine the extent to which Italgas S.p.A. should utilize hybrid bonds relative to S&P Global Ratings' cap, we need to evaluate the maximum allowable hybrid volume under the 15% cap and compare it with the company's existing debt structure, credit metrics, and the market interest rate environment.

1. **S&P Cap Calculation**:
S&P limits the equity credit from hybrids to a maximum of 15% of Total Adjusted Capital (TAC), where TAC = Debt + Equity.
From the 2022 balance sheet:
- Total Equity = 2,390,570,000 EUR
- Total Financial Debt = Long-term financial liabilities (6,402,913,000) + Short-term financial liabilities (142,437,000) = 6,545,350,000 EUR
- TAC = 6,545,350,000 + 2,390,570,000 = 8,935,920,000 EUR
- Maximum hybrid capacity (15% of TAC) = 1,340,388,000 EUR.

2. **Current Leverage and Debt Structure**:
The company's Debt/EBITDA ratio is approximately 4.8x (using Profit Loss From Operating Activities as a proxy for EBITDA at 641,338,000 EUR). For an infrastructure utility, this leverage is moderately high. If Italgas were to maximize its hybrid usage to the 15% cap, it would effectively shift 1.34 billion EUR of debt into equity-equivalent capital. This would drastically reduce its reported leverage, making the 15% cap a highly attractive target for optimizing the balance sheet. S&P's intermediate equity content (50% equity credit) allows companies to use hybrids aggressively up to this cap to manage leverage without diluting shareholders.

3. **Market and Funding Environment**:
In 2022, interest rates rose sharply (Swap curves shifted from negative in 2021 to ~1.7-1.9% in 2022, and corporate spreads widened to 2.3% for IG non-financials). Despite higher absolute costs, hybrids still offer a tax shield compared to pure equity and provide crucial leverage relief for companies undergoing heavy capex (as seen in their massive investing cash outflows of -1.28 billion EUR). An infrastructure player like Italgas with predictable cash flows is well-positioned to service hybrid coupons. 

4. **Optimal Utilization Extent**:
Given the significant leverage (nearly 5x Debt/EBITDA), maximizing the equity credit under S&P's framework is highly desirable to manage ratings headroom. Issuing up to the 15% cap is standard practice for European utilities to optimize their weighted average cost of capital (WACC) and support massive investment programs. Therefore, the company should utilize hybrid bonds fully relative to the S&P cap (100% of the allowable limit).

<answer>100%</answer>