I need to assess the appropriate level of hybrid bond usage in VINCI's capital structure.

**Company Profile Analysis:**

VINCI is a large French infrastructure/concessions company (société anonyme) with:
- Revenue of €62.3B in 2022 (up from €50B in 2021)
- Strong operating profit of €6.5B 
- Net income attributable to owners of €4.3B
- Total assets of €112B
- Total equity of €29.4B
- Significant concession assets (€28.2B in service concession rights)
- Investment-grade profile given its size, stable cash flows from concessions

**Capital Structure:**
- Noncurrent bonds: €20.4B
- Other noncurrent borrowings: €3.2B
- Short-term borrowings: €6.4B
- Lease liabilities: ~€2.1B
- Total equity: €29.4B
- Cash: €12.6B
- Net debt is significant but manageable given cash flow generation

**Cash Flow Strength:**
- Operating cash flow: €9.4B
- Strong and growing, with concession-based revenues providing predictability

**Arguments for Hybrid Bonds:**
1. VINCI has a large, investment-grade capital structure that could benefit from hybrid bonds' equity credit from rating agencies (typically 50% equity treatment)
2. Concession businesses generate stable, predictable cash flows - ideal for servicing hybrid coupon payments
3. The company already has substantial debt; hybrids could help maintain credit ratings while adding financing flexibility
4. Large European corporates like VINCI commonly use hybrid bonds as part of their capital structure
5. The sub-senior delta for non-financial IG is reasonable (~2.3% in 2022), meaning the additional cost over senior debt is manageable

**Arguments against heavy hybrid usage:**
1. VINCI already has strong equity (€29.4B) and generates robust free cash flow
2. The company pays regular dividends and has share buyback programs, suggesting it doesn't desperately need equity-like instruments
3. Rising interest rates in 2022 make hybrid coupons more expensive
4. Hybrid bonds are subordinated and more expensive than senior debt
5. Too much reliance on hybrids could signal financial engineering rather than genuine capital optimization

**Appropriate Level:**
For a large investment-grade infrastructure company like VINCI, hybrid bonds make sense as a moderate component of the capital structure. They're commonly used by European infrastructure/utility companies to optimize credit metrics. However, they shouldn't dominate the capital structure - they're a complementary tool. Given VINCI's strong cash flows, large debt book, and investment-grade profile, a modest allocation (around 25%) of the capital structure to hybrids would be appropriate. This reflects typical market practice for such companies - enough to gain meaningful rating agency equity credit without over-relying on a more expensive, subordinated instrument.

The company's total long-term debt is roughly €23.6B. A 25% hybrid allocation would represent approximately €5-6B, which is a reasonable and common proportion for large IG corporates in Europe.

<answer>25%</answer>