MIL-DTL-24688A
3.3 Construction.
3.3.1 Type II. Construction of Type II materials shall be in accordance with 3.3.1.1 through 3.3.1.5.
3.3.1.1 Class 1. The panel shall consist of a backing conforming to Type I unfaced foam, laminated with
non-perforated fibrous glass cloth facing.
3.3.1.2 Class 2. The panel shall consist of a backing conforming to Type I unfaced foam. One face of the foam
shall be slotted, 3/16 inch wide by 3/16 inch deep, on ½-inch centers, in one direction only. The perforated glass cloth
facing shall be bonded to the slotted side of the foam, installed so that the perforations in the cloth facing are
centered over the slots in the foam (see figure 1).
3.3.1.3 Class 3. The panel shall consist of a backing conforming to Type I unfaced foam, laminated with a
fire-retardant adhesive meeting the fire requirements of MIL-A-3316, to a primer coated aluminized
polyester/aluminum foil reinforced with a fibrous glass scrim.
3.3.1.4 Class 4. The panel shall consist of a backing conforming to Type I unfaced foam, laminated with a
fire-retardant adhesive meeting the fire requirements of MIL-A-3316, to a primer coated aluminized
polyester/aluminum foil reinforced with a fibrous glass scrim laminated to a lightweight fibrous glass cloth.
3.3.1.5 Class 5. The panel shall consist of a backing conforming to Type I unfaced foam, laminated with a
fire-retardant adhesive meeting the fire requirements of MIL-A-3316, to a primer coated white polyester film
reinforced with a fibrous glass scrim.
3.3.2 Type III. Construction of Type III (preformed pipe) materials shall be in accordance with 3.3.2.1 through
3.3.2.1 Class 1. Class 1 material shall be Type I, flexible foam formed into pipe insulation. The insulation
shall be split or slit lengthwise.
3.3.2.2 Class 2. Class 2 material shall consist of foam conforming to Type I, flexible foam formed into pipe
insulation, laminated with adhesive as specified in 3.2.7 and fibrous glass cloth facing conforming to the
requirements of MIL-C-20079, Type I.
3.3.2.3 Class 3. Class 3 material shall consist of 1.5 lb/ft³ (maximum) rigid foam formed into pipe insulation.
The insulation shall be split or slit lengthwise.
3.3.2.4 Class 4. Class 4 material shall consist of foam conforming to Type III, Class 3, laminated with
adhesive as specified in 3.2.7 and fibrous glass cloth facing conforming to the requirements of MIL-C-20079,
Type I.
3.3.2.5 Class 5. Class 5 material shall consist of 3 lb/ft³ (maximum) rigid foam formed into pipe insulation.
The insulation shall be split or slit lengthwise.
3.3.2.6 Class 6. Class 6 material shall consist of foam conforming to Type III, Class 5, laminated with
adhesive as specified in 3.2.7 and fibrous glass cloth facing conforming to the requirements of MIL-C-20079,
Type I.
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