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Many people buy “cello” bags made from Cast PolyPropylene, sometimes referred to as CPP The bags are low priced, sold in the retail stores and are generally “made in China”. These bags do not have the tensile strength or the gas, vapor, moisture barriers of bags made from BOPP and Cellophane. Biaxially Oriented PolyPropylene, BOPP film with superior physical attributes was developed to replace cellophane. Our site sells only BOPP and Cellophane Cello Bags. We do not sell CPP bags.
You can tell the difference between CPP bag and a BOPP Cellophane bag. You can not push your finger through a true BOPP bag. It is strong and stiff. A Cast PolyPropylene CPP bag will elongate when you push your finger through it. This tensile property, elongation, will allow CPP to elongate from 550% to1,000% of the film thickness. 
The resultant bag will have a elongation dimple as in this picture.
You can heat seal a Cello Bag with and iron and it will not melt as easily as a CPP bag. The film is annealed in the manufacturing process which gives the film high temperature stability. Try this with your Cello Bag only if it is a Cello Bag, remember CPP bags will melt on you iron very easily .
All of the bags can be heated sealed with a regular iron or a industrial Impulse Sealer shown in this picture. 
All “True Cello Bag” has a back seam. The back seam is a overlap seam typical of the back seam on snack food bags, such as cookie, cracker, potato chip and peanut bags. Here is an example of a “True Cello Bag” in the square style with a foldover bottom an easy stand up feature”
Depending on the type of film used in the bag, a stack of bags may have a gold tint look. The bags are not old or poor quality. What you are looking at is light diffusion through a stack of bags. If you look at a single bag, it is clear. The film used in making the bag is "Saran Coated". If by chance you have "Saran Wrap tm " in your kitchen cupboard, and you pull out the roll, you will notice it has the same color tint as the bags.
BOPP, Biaxially Oriented PolyPropylene, is a flexible material derived from melting and biaxially orienting (stretching on both axis) a polymer called polypropylene. This raw material is inert and unaffected by most chemical agents occurring in everyday life. It meets the requirements of the US Food and Drug Administration and other relevant authorities throughout the world. Polypropylene contains primarily carbon and hydrogen, and includes no heavy metals or other environmentally hazardous substances. The process of biaxially orienting polypropylene, stretching it in the machine direction and transverse direction, improves the films physical properties, such as water vapor barrier, stiffness, dimensional stability, and optics.
The important properties of Biaxially Oriented Polypropylene BOPP are:
- It has a high tensile strength
- It has a high gloss and clarity
- It has good puncture and flex-crack resistance over a wide range of temperatures
- It is a good barrier to water vapor
- It is resistant to oils and greases
- It is not affected by moisture and does not wrinkle or shrink with environmental changes
Cellulophane film begins life as a natural product - wood. The process of converting wood pulp to film is, however, quite complex. First it undergoes a series of chemical processes to break the pulp down to a viscose liquid.
The viscose is extruded and then cast along a series of rollers and baths, during which a softener is often introduced to provide a measurable amount of strength and flexibility. Chemicals used in the process are reclaimed and recycled.
Un-coated cellulose films are highly permeable to water vapor while still providing an excellent barrier to micro-bacteria, flavors and aromas. They are naturally glossy, anti-static, and heat-resistant. Many grades of film are, however, coated, in order to refine and control these natural attributes for specific applications and for moisture and aroma barrier.
For more information regarding packaging films, you can go to the web sites of ExxonMobil tm and UCB tm films, the largest producers of packaging films in the world
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