# The Accumulating Wrapper The accumulating wrapper is the compounding form of a River position. A lender can hold the position through an ERC-4626 wrapper that collects the class token's coupon and rolls it into the wrapper share price. The economic exposure is the same as the class token, with a compounding product shape. ```mermaid flowchart LR A["Class token
principal + cash coupon"] -- "wrap" --> B["Accumulating wrapper
single growing share"] B -- "unwrap" --> A ``` ## Why use it The wrapper is useful when a lender or protocol wants: * a single balance with principal and coupon combined; * an ERC-4626 read surface for integrations; * automatic reinvestment of funded coupon; * collateral, treasury, vault, or structured-product compatibility. ## Wrapping Wrapping is synchronous. A holder deposits class tokens and receives wrapper shares in the same transaction. ## Unwrapping Unwrapping is cash-first. If the wrapper has earned cash/coupons available for the holder, that portion pays immediately. Any remaining principal exposure moves through the underlying class exit process and keeps earning until paid. :::tip\[Cash-first behavior] If the requested unwrap is fully covered by the holder's earned cash capacity, the exit can settle immediately without joining the class exit queue. ::: ## Transfers When wrapper shares transfer, the economic exposure transfers with them. Unused instant-cash (realized but unclaimed coupons) capacity follows the shares proportionally, so the wrapper remains fair to both sender and receiver. ## Integration surface The wrapper is the default surface for most protocols. It is easier to compose with because it looks like a standard ERC-4626 vault for reads and has a single price that reflects retained income. Developers should read [Wrapper Integration](/integrate/wrapper) and [Wrapper Accounting](/accounting/wrapper) before using it as collateral or routing user funds through it.