**Example
for the case of a packing in folded film covering a product
of regular form.**

**In
order to determinate the amount of Kg of required material for
packing a product, we should know first: **

**1.
Amount of required packages. **

2. Dimension of the product to pack, and consequently, the dimensions
(long, wide and thickness) of the material required for each
package.

3. Material that is going to be used in the packing (PVC, PEAD,
PEBD, PP, CELOFAN, etc.), therefore, its density or specific
gravity, this means, its weight per volume unit of the material
in question.

**For
the calculation, will use the following formula: **

**D
= M/V**

**where:
**

**D
= density of the packing material, in g/cm3. **

M = Mass (weight) of the packing material, in g.

V = Volume of the packing material(long x wide x height (thickness)),
in cm3.

**therefore:
**

**M=DV
**
**or
what it is the same: **

**Amount
of required
material for packing a product = Required packages
number X Length of packing material X Width of packing material
X Height of packing material (Thickness) X Density of packing
material**

** **

Figure 1. Usual form of Shrink film: Rolls of center folded
film.

**We
must remember that in order to obtain appropriate results, we
should use the same units in whole formula, consequently, adapting
the previous formula to the units normally used and to the commonly
used form of presentation of the film (see figure 1), it remains
in the following form:**

**K
= ( N x L x A x C x (2.54/100,000) x 2 x D )/ 1000 **

**where:
**

**K
= Amount of required Kg for packing a product. **

N = Number of required packages.

L = Length of packing material, in cm.

A = Width of required material for each package, in cm (don't
forget add the waste upon sealing and the tolerance of production).

C = Gauge or thickness of packing material, normally specified
in 0.00001" (hundred thousandths of a inch).

(2.54/100,000) = conversion of 0.00001" to cm.

2 = duplication of the volume of used wide A film; this is because
we are using a folded film that cover top and bottom parts of
the product (see figure 3).

D = Density of packing material, in g/cm3. (For PVC=1.35, PEBD=0.92,
PEAD=0.96, etc.)

1000 = conversion of used material, g to Kg.

**Calculating
the amount of PVC shrink film required in order to pack
10,000 packages with the dimensions shown in the following
figure: **

**
**

** **

Figure 2. Measures of the product to packing

**DATA:
**

**1.
N = 10,000 packages. **

2. Dimensions of the product = 40 x 30 x 10 cm, consequently
the dimensions of each packing will be (see figure 3):

** **

Figure 3. Dimensions of the film used in each package.

**Note.
In case of having a product with different dimensions
in both ends, you will use the average value of both ends,
for example, if one side measure 8 cm and the other side
10 cm, the value that will take for calculation will be
9 cm.**

**3.
L = 42 cm. **

4. A = 54 cm. = nominal measure of the utilized roll,
include the looseness of the packing before the shrinking,
that avoid breaks in the seal at the moment of closing
the sealer jaws, as well as the amount of waste required
for a comfortable seal job (2 or preferentially 3 cm).

Including the tolerance added in manufacturing (2.5 cm.),
the total width is 57.5 cm.

5. C = 100 hundred thousandths of inch (recommended for
most of applications).

**Note.
Preferentially, the product to pack will make comfortable
according to the previous figure in order to facilitate
the packing and diminish the waste, that is, the minor
dimension will correspond to the height, for diminishing
the dog ears and the wrinkles in corners; from the other
two dimensions the longer will correspond to the roll
width, for the lower amount of waste (in this case 30
cm instead of 40 cm), but this is not advisable for small
measures (widths lower to 15 cm), because its manufacturing
is hindered. **

**
**

** **

Figure 4. Product packed showing the waste.

**6.
Used material = PVC **

7. Density = 1.35 g/cm3

**Minimum
amount of kilograms required by the customer (you will
be suppose to add the material that considered as waste
in the packing process and 10% additional for possible
variations in width and gauge of the packing material):
**

**K
= ((10,000 x 42 x 57.5 x 100 x (2.54/100,000) x 2 x 1.35)/
1000)*1.1 = **__182 Kg of folded PVC shrink film of 54
cm, gauge 100__

**07/09/2005**