Packaging Reference Library · Technical Reference

Poly Bags and Tubing

Poly bags and layflat tubing are polyethylene films used to protect, contain and bundle products. This sheet compares LDPE, LLDPE and HDPE, explains mil thickness and bag dimensions and lists the common bag styles.

Ref PK-0112ASTM D2103

Draft, open for review. Check every value against the governing standard and the manufacturer’s data before use.

What it is

Poly bags are made by sealing polyethylene film into a bag. Layflat tubing is a continuous film tube on a roll. The user cuts it to length and seals one or both ends, which suits odd-length products. Bag film is made from LDPE (low-density), LLDPE (linear low-density) or HDPE (high-density) polyethylene, or blends. Film thickness is given in mils: 1 mil is 0.001 in, or 25.4 microns. See the film gauge conversion chart. ASTM D2103 covers polyethylene film and sheeting specifications.

How to measure

Measure the width of the bag opening, inside, flat.
Measure the length from the opening to the bottom seal.
For gusseted bags, give width plus gusset, then length. For example, 10 x 8 x 24 means a 10 in face, 8 in total gusset and 24 in length.
Allow room for the product's depth. A thick product needs a wider flat bag or a gusseted bag. Test with a sample.
Give the thickness in mils.

Resin comparison

Resin	Feel and look	Strengths	Typical uses
LDPE	Soft, clear, flexible	Clarity, easy sealing	General parts bags, food bags, layflat tubing
LLDPE	Soft, slightly less clear	Puncture and tear strength at lower gauge	Heavier parts, can liners, stretch film
HDPE	Crinkly, hazy, thin	High strength at very low thickness	Produce bags, light liners, deli bags

Bag styles

Style	Features	Notes
Flat open-top	Simplest bag	Seal by heat or tape
Reclosable zipper	Press-to-close track	Size given excluding the zipper area on many lines
Slider	Zipper with slider	Easier for gloves
Gusseted	Expands for boxy products	Order by face, gusset and length
Bags on a roll	Perforated for tear-off	Fits dispensers and auto-baggers
Anti-static (often pink)	Static dissipative	Electronics; not shielding by itself
VCI	Vapor corrosion inhibitor	Protects metal parts in storage

Key points

Ask what goes in the bag, its weight and sharp edges, and whether it is food contact.
Food contact bags need resin that meets FDA requirements. Ask for the maker's statement.
Thicker is not always better. LLDPE at lower gauge can outperform thicker LDPE.
Static shielding bags are a different product from pink anti-static bags.

Common mistakes

Measuring the product instead of the bag inside size.
Forgetting the zipper area when quoting reclosable bag length.
Selling pink anti-static bags for parts that need static shielding.
Quoting gusseted bags without the gusset size.

Governing standards: ASTM D2103 (polyethylene film and sheeting). FDA food contact requirements where applicable.

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.

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