To determine the extent to which Bouygues should utilize hybrid bonds relative to S&P Global Ratings' cap, we need to compare the company's current capital structure and financing needs to the 15% cap on equity credit.

1. **Calculate S&P's Cap**: S&P limits the equity credit of hybrids to a maximum of 15% of Total Adjusted Capital (defined as Debt + Equity).
Using the 2022 year-end figures (2023-01-01):
- Total Equity = 13,932,000,000 EUR
- Total Financial Debt = Long-term borrowings + Current borrowings + Current overdrafts = 11,586,000,000 + 1,361,000,000 + 418,000,000 = 13,365,000,000 EUR
- Total Adjusted Capital = 13,365,000,000 (Debt) + 13,932,000,000 (Equity) = 27,297,000,000 EUR
- Maximum Equity Credit (15% Cap) = 27,297,000,000 * 15% = 4,094,550,000 EUR.

2. **Assess Current Hybrids & Context**: Bouygues has no hybrid bonds currently reported in its debt breakdown. They have standard long-term and short-term borrowings, along with lease liabilities. This means they have 0% of the cap utilized and a full 4.09 billion EUR of room under the S&P threshold. 

3. **Strategic Need**: 
- Bouygues experienced a massive increase in Net Debt in 2022 (from 941M EUR to 7.44B EUR), driven largely by a spike in investing activities (6.27B EUR cash used to obtain control of subsidiaries, likely Equans). 
- The market data shows sharply rising interest rates in 2022 across the swap curve and corporate bond indices. 
- Despite rising rates, the average yield on the iShares Core Euro Corp Bond remains relatively modest (~1.085%), while sub-senior delta yields are higher (~2.295%). 
- Because Bouygues has depleted its cash and substantially increased its debt load for acquisitions, it is a prime candidate to issue hybrid bonds. Hybrids would allow the company to raise substantial capital to fund capex and restore its balance sheet leverage ratios (like Net Debt/Equity), while receiving 50% or more equity credit from S&P (thus not hurting its credit metrics), staying comfortably under the 15% cap. 

Given their large acquisition, increased debt leverage, 0% current hybrid utilization, and ample room under the 15% cap, Bouygues should moderately but significantly utilize hybrid bonds to optimize its capital structure and manage its credit rating without exceeding the threshold. A 50% utilization relative to the cap represents a robust, strategic use of this instrument to refinance/anchor the balance sheet after the Equans acquisition.

<answer>50%</answer>