Caulk is generally used in exposed areas where appearance is critical, but foam can also be trimmed and painted. Table 2 shows which foam to use where. In crawlspaces, a two-component kit is convenient for both insulating and sealing because use of machines in such confined spaces is messy and uneconomical. One sealable area often missed is the stud space above a cold air return. It must be sealed because the cold-air return system will not work properly if it is not a closed loop.
Builders often omit the wood blocking between the studs and above the grille.
These kits are also useful in attic spaces where restricted movement and awkward access make locations difficult to seal. Another important use for the two-component kit is sealing between the stud spaces at the perimeters of drop ceilings. The material mix is ejected from the container as a sticky bead. If the cavity is too big, two applications may be needed to make sure there is enough moisture available to cure the foam. Fast-cure systems are available, which may be tack free in just ten minutes.