Thicker plastic for sharp or heavier items (often labeled as B34P4 ).
If you are referring to technical or construction "Zip" systems, here are the most relevant guides: Installing ZIP System Sheathing: Taping Seams and Corners B34zip
These bags are standard reclosable plastic bags primarily sold by JPB Jewelry Box and similar industrial suppliers. 3 inches by 4 inches. Material Types: Thicker plastic for sharp or heavier items (often
Commonly used for organizing jewelry, small electronic components, craft supplies, and hardware. Alternative Interpretations small electronic components