The primary reason that insulation saves you money over time is that it reduces your energy bills by making your home more energy efficient. A crucial part of an insulation system is a properly installed vapor barrier. Local building codes dictate whether your insulation requires a vapor barrier based on the type installed. While some high-quality wool insulation may not technically need a vapor barrier, most municipalities still require one to meet code.

Radiant barriers and insulation serve different purposes, so one is not inherently better than the other. Radiant barriers reflect radiant heat, helping keep spaces cool, especially in hot climates, while insulation slows heat transfer through conduction. For optimal energy efficiency, it’s best to use both together. 

Radiant barriers can enhance the performance of insulation by preventing heat gain in the summer and heat loss in the winter. The choice between them depends on specific climate conditions and the building’s design requirements.

While not every wall requires a vapor barrier, if you do need one and don’t install it, moisture can get between the walls of your home. This can lead to water damage from mold growth or rot, and the excess moisture could also attract pests, including termites, cockroaches, or ants.

Unfaced wall insulation is easier to cut and install, making it the better choice for a DIY project. It’s also more affordable. But if it’s unfaced, you’ll likely need to add a vapor barrier to reach your desired R-value and efficiency, as it doesn’t offer any moisture barrier.

Faced insulation uses paper or foil to create a built-in barrier and doesn’t require an extra step. It’s also more fire-resistant and safe. But it’s quite a bit more expensive and a little bit harder to work with as a DIYer.