Flexible Packaging Glossary

Bags on a Roll: Polyethylene bags can put up on 3" cores and perforated between the (side) seals or between the (bottom) seal and the opening of the next bag to facilitate dispensing of the bags.

Bottom Gusset: A bottom gusset is formed by pushing the bottom, closed end of a flat poly bag up, into the bag interior making an accordion type fold or pleat at only the bottom of the bag. Bottom gusset bags are always sidewelded. The size of the bottom gusset is measured across the open or unfolded dimension. The bottoms of plastic bags constructed in this manner sit more or less flat on a surface when filled.

Bottomseal: Poly bags that have a heat seal across the width at the bottom of the bag are manufactured by making a seal about 1/4" up from the bottom.

Flat bag: A flat plastic bag is the most basic poly bag construction. Flat bags have no gussets (folds or pleats). Flat poly bags can be either sidewelded or bottomsealed. Flat bags have a width and a length dimension and one open end measured across the width. Sleeves are poly bags with two opposing open ends.

HDPE: High Density PolyEthylene.

Header Seal:
A header seal is heat sealed across the width of the bag, usually near the top. Many custom poly bags used at point-of-purchase displays have been loaded from the bottom and sealed by the company that packages the product. A header seal keeps the contents of the bag from rising to the top of the bag and interfering with the hang hole or being obscured by printing in the header area. For small quantities or more flexibility to make changes on printed headers, a cardboard header with a hang hole can be used, but making plastic bags with a header seal as an integral part of the bag is more cost effective at larger quantities.

LDPE: Low Density PolyEthylene. Most of the custom flexible packaging items we manufacture are made from this plastic film.

Mil or Thickness: The term "mil" is sometimes used in reference to the thickness of the polyethylene film. It expresses thousandths of an inch as a whole number. Thus, 1.5 mil is one and one half thousandths of an inch or .0015". When this measurement is included in a bag dimension, it refers to the thickness of the film for one side of a bag.

MVTR: Moisture Vapor Transmission Rate. This is a measurement of how quickly moisture and air will pass through the plastic film. It varies depending on the type of resin used to extrude the film, the thickness, and the film's ambient environment.

PP: PolyPropylene. The Polypropylene we use to manufacture flexible packaging is a mono layer, random co-polymer containing ethylene. It is a better barrier to moisture and air transmission than either LDPE or HDPE (see "MVTR"), but not as complete as the stiff, crystal clear PP that is similar to cellophane.

Recloseable or polyethylene zipper lock: Polyethylene bags can be made with narrow interlocking tracks, made from the same plastic material, that are sealed into the poly bag near the open end across the width. These are called zipper bags, zip lock bags or reclosables. Once the bag has been filled, the user then pinches one end of the track near the seal at the side and slides their fingers across the width of the bag, forcing the poly zipper tracks to merge and lock together. Zip lock bags can be opened and resealed a number of times. Plastic bags can also be made "tamper evident". One way to do this is to manufacture the bag pre-closed above the ziplock, with or without a perforation and loaded from the bottom. The final heat seal is then made at the bottom to enclose the contents after loading. Another type of tamper evident ziplock bag has a zipper that will not open once it has been closed except by destroying the bag itself.

Side gusset: A side gusset is formed by pushing the side edges of a flat poly bag into the bag interior, making an accordion type fold along both sides of the bag. Side gusset bags are always bottomsealed. The size of the side gusset is measured across the open or unfolded dimension. Plastic bags constructed in this manner conform well to box-like shapes.

Sideweld: Bags that have a heat sealed edge along the length of each side are manufactured by sealing the sides.

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