R-23 vs R-38 Insulation: Which Do You Need? Choosing between R-23 and R-38 insulation is a common decision for DIY eco-builders deciding where to spend limited budget and how to size wall and attic assemblies. This comparison of r23 vs r38 insulation explains where each R-value is typically used, how common materials reach those targets, and practical trade-offs (space, cost, moisture, and performance) so you can pick the right assembly for your build or retrofit. TL;DR: - R-23 is the typical target for 2x6 framed exterior walls and small retrofit cavities; it's achievable with standard batts or layered rigid foam and is cost-effective for wall assemblies. - R-38 is the common attic/ceiling target in many climate zones (often ~10–13 inches of fiberglass or cellulose); choose it when floor/ceiling heat loss dominates or you need much lower heating loads. - Use high R/inch materials (closed-cell spray foam or rigid polyiso) when depth is limited; always pair with air sealing, continuous ...