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Consider the following binder:

enter image description here

Such binders are usually made of a single plastic sheet. The sheet is flexible and durable as you open/close the binder. I think they're formed into their U shape by a heat gun. Such binders are not to be confused with the vinyl binders that wrap a flexible vinyl around a solid thick core of wood or cardboard.

My question is: what kind of sheet this? Under this question, we may get the following sub-questions:

  • If there are multiple materials that are usually used for the same purpose, what are they, and what are their pros and cons?
  • What's usually the thickness of such sheets?

What I've done so far:

  • This seems to say that the material is either polyethylene or polypropylene.
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  • What's the intended purpose/use case for this question? What do you plan to create using this material?
    – Allison C
    Commented Aug 16, 2022 at 19:00
  • @AllisonC - create a binder that I'll be holding by my hand and walk with it outdoors, with important documents inside it. So it will have to survive my sweaty hands, rain drops, sun and the outdoor atmosphere in general, all while protecting items inside (e.g. items within should not become wet should the outer cover get wet). Since carried by hand, it better be compact and lightweight with a reasonable cost (e.g. carbon fibre is not acceptable).
    – caveman
    Commented Aug 17, 2022 at 15:58
  • 2
    Okay. Why does simply purchasing a ready-made binder not meet your needs? This kind of information will help people get the right answer to this question.
    – Allison C
    Commented Aug 17, 2022 at 16:09
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    @AllisonC - Because of the specific design of the binder. E.g. the way it is partitioned from within. It has a unique partitioning that meets my requirements better than any binder that I found ready-made in the market. I surveyed the market a lot before deciding that I have to make my own.
    – caveman
    Commented Aug 17, 2022 at 16:33
  • It seems some are made of PE and some PP. Both materials are good for this purpose, but both are hard to bond to if your plan was to use adhesive. Bonding is normally done by heat welding, or using fasteners. I doubt there's a standard thickness.
    – fixer1234
    Commented Aug 18, 2022 at 16:30

1 Answer 1

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The question is pretty much answered within the question. The link in the question is to an article by a supplier, and focuses on the binders that supplier offers. But the article seems pretty comprehensive, and consistent with all of the similar binders I've seen. So this answer will mainly summarize and confirm information in the provided link.

  • What kind of material is used to make poly binders? Polyethylene appears to be the predominant material, with polypropylene used for some.

  • What are the pros and cons of the different materials?

    Either material can provide the right compromise of stiffness vs. flexibility in a good thickness for a binder. They both offer appropriate mechanical strength and durability to hold the ring mechanism without it tearing out, to open and close over a long service life without fatiguing and splitting, and to hold up to the wear and tear of use. Both are washable to keep them clean, and waterproof to shield the contents from splashed liquid and not be affected by perspiration when handled.

    Both are inexpensive plastics that are readily available in sheet form, and easy to handle in the manufacturing process (e.g., cutting, attaching the ring mechanism, folding, etc.).

    It isn't obvious why polyethylene is more commonly used (cheaper?, better characteristics? more readily available?).

    There appear to be a few reasons for selecting one material over the other:

    • The stiffness/flexibility differences might allow use of a better thickness material to meet the requirements for a specific binder.
    • Polypropylene appears to be the choice for custom colors (perhaps easier to color, or the colored sheet material is more readily available?).
    • Polyethylene appears to be used for applications that require frequent sanitizing (e.g., medical or veterinary settings).
  • What is the sheet thickness? The linked supplier offers poly binders in four thicknesses from 23 gauge to 75 gauge, which ought to be roughly consistent with competitors' products. There is no standard for binder thickness and no need for a custom-made thickness, so the increments are probably common thicknesses that are readily available. The different thicknesses affect cost, stiffness, and durability. I'm not sure what this particular "gauge" reference translates to. I happen to have a poly binder laying around, and its thickness is about 0.5 mm or roughly 0.02 inches.

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