Desiccants: Cover Stock Data

Table 1: MVTR
Table 2: Unit Calculation Charts

A well-designed package is usually protected by a barrier film, such as polyethylene, preferably with a low moisture vapor transmission rate (MVTR). The MVTR of the barrier depends upon the type and thickness of the materials used and the external environmental conditions.

Table 1 provides the MVTR for a number of barrier materials. Knowing the MVTR (in grams of water per square foot per day), the total surface area of the barrier (package surface area) and the length of time in storage, you can calculate the amount of moisture penetrating the package over time. This moisture must also be removed by the desiccant to protect against possible condensation within the package or damage to the product due to the high humidity.

Table 1: MVTR of Common Cover Stock Materials

    MVTR*
MVTR* Material gm/m2-day gm/ft2-day
Aluminum Foil Wrapping 0.025 mm 0.5 00.5
Aluminum Foil Wrapping 0.009 mm 1.0 0.09
Cellulose Films ('Cellophane')
400's MXXT Grade (Polyvinylidene Chloride Coated) Polyvinylidene/Polyvinyl Chloride Films ('Saran') 0.005 cm (0.002 in)
1.5 0.14
Polyethylene Films ('Polythene')
0.0125 cm (0.005 in) Waxed Paper
(45.5 kg (100 LB) per DC Ream)
4.0 0.37
Cellulose Films ('Cellophane')
300's MSAT Grade (Cellulose Nitrate Coated)
7.5 0.70
Glassine Lacquered
(16 kg (35 LB) per DC Ream)
9.0 0.84
Polyethylene Film ('Polythene')
0.005 cm (0.002) in)
10.0 0.93
Polyethylene Film ('Polythene')
0.0025 cm (0.001 in)
20.0 1.86
Polyethylene Coated Kraft
(9 kg (20 LB) per DC Ream)
30.0 2.79
*Determined at 100°F and 90% RH

Table 2: Unit Calculation Charts

Flexible Barriers (Chart 1)
Rigid Containers (Chart 2)

FLEXIBLE BARRIERS
(Chart 1)

AREA IN
SQUARE FEET
AREA IN
SQUARE INCHES
UNITS
REQUIRED
.1 30 1/6
.3 45 1/3
.6 90 1/2
1.3 180 1
1.9 270 2
2.5 360 3
3.1 450 4
3.8 540 5
4.4 630 6
5.0 720 7
5.6 810 8
6.3 900 9
7.5 1,080 10
8.8 1,260 12
10.0 1,440 14
20.0 2,880 16
50.0 7,200 32
100.0 14,400 80
120.0 18,000 160
150.0 22,500 200
180.0 27,000 250



RIGID CONTAINERS
(Chart 2)

VOLUME IN
GALLONS
VOLUME IN
CUBIC FEET
VOLUME IN
CUBIC INCHES
1.1 .14 237
2.1 .28 476
3.2 .42 714
6.2 .83 1,428
12.5 1.67 2,856
18.7 2.50 4,284
25.0 3.33 5,712
31.2 4.16 7,140
37.4 5.00 8,568
43.6 5.83 9,996
50.0 6.66 11,424
56.1 7.50 12,852
62.3 8.33 14,280
74.8 10.00 17,136
87.3 11.66 19,992
99.7 13.32 22,850
199.4 26.64 45,700
498.5 66.65 114,250
997.0 133.30 228,500
1,240.0 166.00 285,500
1,550.0 207.00 357,000

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