You can put a number of things under vinyl siding, but one of the most popular options is to use foam insulation. This will help to protect the home from drafts and keep it insulated. You can also use metal flashing if you are installing your siding over wood, as this will help to protect the wood from moisture damage.

Vinyl siding should be installed over a water-resistant barrier, such as building paper, Vycor cement board, or asphalt felt. If you are using insulation, it is recommended to install the insulation before installing the vinyl siding.