Ferrovial SA’s financial structure is heavily influenced by its infrastructure project model, which constitutes the majority of its noncurrent assets (13.67 billion EUR out of 18.87 billion EUR). These infrastructure projects are long-term, capital-intensive, and typically financed with long-term, project-specific debt (10.78 billion EUR in noncurrent other borrowings, with 7.89 billion EUR specifically related to infrastructure).

Key factors in assessing the reliance on hybrid bonds:
1. **Interest Rate Environment:** The swap curves (5Y, 7Y, 10Y) shifted from negative or near-zero territory in 2020-2021 to approximately 1.7-1.9% in 2022. This increasing interest rate environment makes traditional debt more expensive to service.
2. **Current Equity and Debt Position:** Ferrovial maintains a solid liquidity position (5.13 billion EUR in Cash and Cash Equivalents). However, the company relies significantly on Non-recourse debt for its infrastructure projects, which isolates risk at the project level.
3. **Hybrid Bond Utility:** Hybrid bonds (often treated as equity for credit rating purposes) provide a middle ground for companies seeking to optimize their balance sheets without diluting existing shareholders through equity issues. Given Ferrovial’s heavy capital expenditure requirements for long-term infrastructure projects, moderate reliance on hybrids helps maintain investment-grade metrics while managing financial leverage.
4. **Current Capital Structure:** With equity attributable to owners of the parent at 4.11 billion EUR and noncurrent borrowings at 10.78 billion EUR, the company is not overly burdened but must manage the cost of capital effectively. 

A 25% reliance on hybrid instruments within the long-term financing stack is a prudent strategy for a major infrastructure player in a rising interest rate environment. This provides "equity credit" to support credit ratings while allowing for the tax-deductibility or operational flexibility that pure equity does not offer, without over-leveraging the entity with high-coupon hybrid debt.

<answer>25%</answer>