What type of insulation is commonly used in walls?

Fiberglass batts and spray foam are the most commonly used types of insulation for walls due to their effective thermal resistance properties. Fiberglass batts are pre-cut panels that are easy to install in standard wall cavities, making them a popular choice among builders and DIYers. They provide good insulation with a high R-value per inch, which measures insulation's effectiveness in resisting heat flow. Additionally, spray foam insulation expands upon application, filling gaps and creating an air-tight seal that can significantly enhance energy efficiency in both new constructions and renovations. This versatility and effectiveness make fiberglass batts and spray foam the standard in wall insulation.

While cellulose and wool, plywood and drywall, or straw bales and cork have their merits and specific applications, they are not as widely utilized in typical wall insulation scenarios as fiberglass batts and spray foam.