What is a disadvantage of perlite and wood fiber?

The statement that they have low R-values and can hardly stand alone accurately highlights a significant disadvantage of perlite and wood fiber as insulation materials. R-value is a measure of thermal resistance; materials with low R-values may not provide adequate insulation on their own, meaning they might not effectively reduce heat transfer. This necessitates the use of additional insulation layers or different materials to achieve acceptable energy efficiency in a roofing system. Therefore, while perlite and wood fiber can be useful in certain applications, their low R-values limit their effectiveness as standalone insulation solutions, making it necessary to consider their limitations when selecting materials for roofing projects.