Poly Bag Consumption and Costing

Polybag or plastic bag is an essential packing accessories used for containing garments into it. Polybag is a thin flexible film made from polymerized distinct monomer unit. It is used to protect and or preserve garments during shipping and storage. It may also provide information about when garment goods are sold to consumers.

Types of Poly Bag

There are different types of poly bag used in garment packing which are as below;

1. Heat sealed tube
2. Re-closeable with
1. Self adhesive
2. Button
3. Zipper
3. Flapped
4. Gusseted
5. Hanger

Types of Poly Film Materials 
Almost all plastics can be formed into a thin film, some of them are

Polyethylene
Polyethylene is a light, versatile synthetic resin produced from the polymerization of ethylene. Polyethylene may be classified according to its density and branching. The three main types are High-density polyethylene (HDPE), Low-density polyethylene (LDPE), and Linear Low-density polyethylene (LLDPE). As an apparel packaging accessories LDPE is mostly used.

Polypropylene
Polypropylene is also a synthetic resin produced from the polymerization of propylene. Polypropylene is classified according to orientation. The two main types are Cast un-oriented polypropylene (CPP), and Biaxially oriented polypropylene (BOPP). As an apparel packaging accessories BOPP is mostly used.

Point of difference	Polypropylene	Polyethylene
Monomer	Propylene	Ethylene
Abbreviation	PP	PE
Clarity	Semi-crystalline	Inert, translucent
Hand	Stiff and Hard	Soft and Pliable
Melting Point	130 to 171 °C	115–135 °C
Chemical Formula	(C3H6)n	(C2H4)n
Density	0.85–0.94 g/cm3	0.88–0.96 g/cm3
Cost	Cheap	Expensive
Barrier	Good to vapor, moisture	Not good as PP

Co-polymer 
For better utility and practical value poly bag may be produced from copolymerized materials like polypropylene co-polymer.

Polybag consumption
Polybag is sold in weight of either Kg or Lb, which is derived from the volume and density of a specific polymer.

Weight = Volume* X Density**

*Volume
Volume refers to the product of the Length, Width, and Thickness of a poly film. Film thickness plays a significant role in polybag consumption which is a little bit difficult to understand.

Poly film Thickness
There are many systems used to measure the thickness of poly film including Gauge, Mil, and Micron but the gauge is widely used.

Gauge refers to one-hundred-thousandth of an inch (1/100,000) or 0.00001 inch
Mil refers to one-thousandth of an inch (1/1,000) or 0.001 inch
Micron refers to one-thousandth of mm (1/1,000) or 0.001 mm

Though the thickness measuring unit of the poly bag is different than linear measurement, a unique measurement unit is necessary for volume calculation. 

1	Inch	CM	MM	Mil	Micron	Gauge
Inch	1	2.54	25.40	1000.00	25400.00	100000.00
CM	0.3937	1	10.00	393.7007	10000.00	39370.0787
MM	0.03937	0.10	1	39.37	1000.00	3937.00787
Mil	0.001	0.002540	0.0254	1	25.40	100.00
Micron	0.00003937	0.0001	0.001	0.039370	1	3.9370
Gauge	0.00001	0.0000254	0.000254	0.01	0.254	1

**Density
Density refers to the mass per unit volume of specific polymer types. There are different types of polymers used for poly bagging including HDPE, LDPE, LLDPE, CPP, BOPP, etc. each of them has a specific mass which is measured either in gram or ounce per cubic inch and/or CM. 

Poly Bag Materials	Mass Per Cubic CM		Mass Per Cubic Inch
	Gram	Ounce	Gram	Ounce
HDPE- High Density Polyethylene	0.94	0.033158	15.4038	0.543355
LDPE- Low Density Polyethylene	0.92	0.032452	15.0761	0.531795
LLPE- Linear Low Density Polyethylene	0.92	0.032452	15.0761	0.531795
PP- Polypropylene (Homo-polymer)	0.90	0.031747	14.7484	0.520233
PP- Polypropylene (Co-polymer)	0.90	0.031747	14.7484	0.520233

Poly bag costing
Poly bag costing depends on its weight, types, materials, messages on it, and other specification.

Cost = Volume X Density X Lot size X Unit cost 

Poly bag costing formula

Formula-1: 
Cost = (L” X W” X T” X D X 2 X Qty X $ @ Kg) / 1000

Where,
L   = Length
W = Width (Tube)
T  = Thickness
D  = Density (gram per cubic inch)
2  = no. of fold
1 Kg = 1000 Grams

Problem,
Type = LDPE
Length = 20 inch
Width = 10 inch (Tube)
Thickness = 160 gauge (0.00160 inch)
Density = 15.0760 gram per cubic inch
Order Qty = 24,000 pcs.
Unit price = $2.00 per kg
Total cost = ?

Solution, 

Total cost = (L” X W” X T” X 2 X Gram per cub. Inch X Qty X $ @ Kg) / 1000

                = (20 X 10 X 0.00160 X 2 X 15.0760 X 24000 X $2.00) / 1000
                = $463.13

Formula-2: 

Cost = (Length” X Width” X Gauge X  Qty X $ @ Kg) / 33,00,000

Problem,
Type = LDPE
Length = 20 inch
Width = 10 inch (Tube)
Thickness = 160 gauge
Order Qty = 24,000 pcs.
Unit price = $2.00 per kg
Total cost = ?

Solution, 

Total cost = (L” X W” X Gauge X Qty X $ @ Kg) / 33,00,000

                  = (20" X 10" X 160 X 24000 X $2.00) / 33,00,000
                  = $465.45

What is 3300 in Poly Bag Formula?

3300 is a factor used for a quick calculation, which is the product of gauge per inch and inverse value of two-fold mass per cubic inch of poly film in grams. This factor is applicable to LDPE only.

To know the derivation of 3300, tap on the below link 

https://apparelmerchandisinglearner.blogspot.com/2020/02/what-is-3300-in-polybag-formula.html