Fanfold refers to the shape of the foam board. To create fanfold insulation, a single layer of the material is folded in on itself into a fan-like shape, compressing the material and making many layers out of one surface. This quality of fanfold board makes for easier transport and packing before it is unfolded for installation. Fanfold underlayment materials are thin layers of foam that resemble cardboard but are made out of plastic materials that stop heat from passing through them.
Uses of Fanfold
Because fanfold board is so thin, it can be used in a number of construction projects in which space is limited but a thin layer of insulation can still add greater thermal resistance. Fanfold board can be installed as part of siding projects, drywall installation, remodeling or house retrofitting. The boards are glued down with an adhesive. Some versions are even peel-away with adhesive already included.
Rigid foam boards are the wider category of foam insulation to which fanfold board belongs. Any type of foam board is a type of rigid foam insulation. Rigid foam boards are easier to install than spray foam and can be used as underlayments for surface materials such as walls, siding and flooring. While fanfold board is thin and comes folded up into layers, other rigid foam board is thicker and heavier and comes stacked in larger panels. Rigid board insulation still has layers of foam, but they are not as flexible as fanfold material and are covered with thicker, cardboard-like outer shells.
Other types of foam board insulation are too thick for the same type of stacking that fanfold boards allow. This can add increased costs for transportation, but the thicker boards also provide greater insulation against the elements. For example, a worker might install fanfold layers to level a surface for later siding or tile installation. However, if keeping heat from entering or exiting the wall is a top priority, the worker could switch to thicker rigid foam board instead. In another difference, some versions of fanfold board have plastic membranes for moisture control, while rigid foam panels often need a plastic membrane to be installed separately.