Isobutylidenediurea (abbreviated IBDU) is an organic compound with the formula (CH<sub>3</sub>)<sub>2</sub>CHCH{NHC(O)NH<sub>2</sub>}<sub>2</sub>. It is a derivative of urea (OC(NH<sub>2</sub>)<sub>2</sub>), which itself is highly soluble in water, but IBDU is not. It functions as a controlled-release fertiliser owing to its low solubility, which limits the rate of its hydrolysis to urea, which is a fast-acting fertiliser.
It is produced by the condensation reaction of isobutyraldehyde and two equivalents of urea:
The controlled-release process is the reverse of the above reaction, which only occurs after the IBDU dissolves.
A number of CRF's have been developed based on urea. Related to IBDU is crotonylidene diurea (Crotodur). Simpler are various urea-formaldehyde materials such as ureaform, which consists of methylene diurea and dimethylene triurea.