  We give a combinatorial model for the exchange graph and g-vector fan
associated to any acyclic exchange matrix B of affine type. More specifically,
we construct a reflection framework for B in the sense of [N. Reading and D. E.
Speyer, "Combinatorial frameworks for cluster algebras"] and establish good
properties of this framework. The framework (and in particular the g-vector
fan) is constructed by combining a copy of the Cambrian fan for B with an
antipodal copy of the Cambrian fan for -B.
