OCaml’s uniform representation enables parametric polymorphism but it comes at a performance cost. For example, the representation of a pair of 32bit integers on a 64bit machine requires 10 words of memory and 2 indirections to get to the actual integers. Unboxed types give the programmer more control of the memory layout of their data, at the cost of the convenience and re-use of parametric polymorphism. We propose a talk to describe our work on adding unboxed types to OCaml, as illustrated by our existing RFC1 and it’s associated description of the unification algorithm2.