A reinsurance sidecar is a special purpose vehicle (SPV) that provides additional underwriting capacity to a reinsurer — typically for one year — by taking a proportional share of a defined book of business. ILS investors provide the capital; the reinsurer provides the underwriting and infrastructure. Both parties share premiums and losses in proportion to their contribution.
Why sidecars exist
Sidecars typically emerge in hard market conditions — following major catastrophe events when reinsurance capacity is scarce and pricing is elevated. By forming a sidecar, an established reinsurer can expand its writing capacity without permanently growing its balance sheet. Investors gain access to a seasoned underwriter's book at attractive pricing without needing to build an insurance operation from scratch.
How they're structured
The SPV is typically domiciled in Bermuda or the Cayman Islands. The reinsurer cedes a quota share of a specific portfolio into the sidecar — for example, 20% of their property catastrophe excess-of-loss book. The sidecar receives 20% of the premiums and pays 20% of any losses. At year end, the vehicle winds down and returns remaining capital plus profit (or loss) to investors. Some sidecars run for multiple years if conditions remain favourable.
Who creates sidecars
The largest sidecar programs have historically been launched by Bermuda reinsurers with strong underwriting franchises — RenaissanceRe, Arch Capital, Everest Re, and Lancashire. After Hurricane Katrina (2005) and again after Harvey, Irma, and Maria (2017), the number of sidecar launches spiked as reinsurers sought to deploy third-party capital at peak market pricing.
Sidecars vs cat bonds
Where a cat bond transfers specific named perils via a single SPV with capital-market-style distribution, a sidecar takes a broad proportional share of a reinsurer's actual written portfolio. This gives investors true diversification across perils and geographies but with less transparency into individual risk details. Cat bonds are typically rated and exchange-listed; sidecars are private, illiquid, and available only to institutional investors.