To determine the extent to which Bouygues SA should utilize hybrid bonds, we first analyze their capital structure as of the end of 2022:

1.  **Total Capital Calculation**:
    *   **Equity**: 13,932,000,000 EUR
    *   **Debt**: We calculate total debt as the sum of "Longterm Borrowings" (11,586,000,000) and "Current Borrowings and Current Portion of Noncurrent Borrowings" (1,361,000,000) and "Current Overdrafts and Short Term Borrowings from Banks" (418,000,000) = 13,365,000,000 EUR.
    *   **Total Adjusted Capital (Debt + Equity)**: 13,932,000,000 + 13,365,000,000 = 27,297,000,000 EUR.

2.  **S&P Hybrid Cap**:
    *   The S&P limit for equity credit on hybrids is 15% of the total adjusted capital.
    *   Limit = 0.15 * 27,297,000,000 = 4,094,550,000 EUR.

3.  **Financial Context**:
    *   Bouygues has significantly increased its net debt (from 941 million EUR in 2022 to 7,440 million EUR in 2023).
    *   The market environment in 2022 saw a substantial rise in swap rates (e.g., 10Y swap curve moved from 0.053% in 2021 to 1.927% in 2022) and corporate bond yields, increasing the cost of debt financing.
    *   Given the significant increase in debt and the rising interest rate environment, hybrid bonds represent an efficient mechanism to bolster the balance sheet while maintaining or improving credit metrics through partial equity classification by rating agencies. Utilizing the full capacity allowed by S&P (100% of the 15% cap) provides the maximum possible benefit to the firm's capital structure stability in the face of rising costs and higher leverage.

<answer>100%</answer>