Structural insulated panels are mold and mildew-resistant by design, and can be used to build structures with the same properties. SIPs are free of cavities, so there’s nowhere for moisture to build up on the panels. This essentially makes them mold and mildew-resistant. When constructed properly, SIPs create airtight seals and structures that prevent moisture infiltration and build up. Without a moist environment, mold and mildew can’t grow.