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I just bought a 260 GSM photo paper (it is used to get photographs printed).

But I was really surprised to find out that it feels thinner as compared to my 250 GSM art papers. I expected that it would feel at least similar to my art paper's thickness, but it feels thin.

Both are A4 papers. If I try to hold the art paper horizontally (parallel to ground) from one side in one hand, it doesn't bend easily due to gravity. It bends but it feels thick.

But I tried same for this photo paper and it bent easily. It also visually looks tiny bit thin as compared to the art paper.

So I'm really curious if I actually got a 260 GSM photo paper or I got a wrong (e.g. less GSM) paper.

Or this difference can be because art and photo papers are for different things? So the GSM varies? Or GSM unit is constant irrespective of paper?

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  • One thing to consider is that paper also has grain. If you fold a piece along the grain, you'll get an easy, sharp bend, while folding across the grain will create more irregularities. By the same token, it will bend differently in the manner you've described.
    – fred_dot_u
    Commented May 4, 2022 at 20:37

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GSM is Grams per Square Meter, so yes, GSM is constant irrespective of the type of paper.

For an A4 format that might be difficult to judge by hand, however, since that would be little less than a 16th of a square meter, which, for 260 GMS, would weigh a little over 16 grams:

260 / ((100x100cm)/(21x29.7cm)) ≈ 260/16.033 ≈ 16.22

The elasticity of paper has nothing to do with the weight (within practical limits :), but with things like the fibre density, the coating, other additives, &c.

But since for all I know you have a high sensitivity for feeling weights, another option of course is that the package was incidentally wrong.

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    I think a really good way to actually verify (in my case) would be to weigh them. And find out which is more closer to 16 grams.
    – Vikas
    Commented May 5, 2022 at 2:47
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    To add clarification for an aspect discussed offline in chat: the weight specs (GSM or pounds), refer to the net weight of the finished product, including any coating, rather than the weight of just the paper substrate (confirmed via several suppliers), contrary to what I suggested in a now-deleted comment.
    – fixer1234
    Commented May 10, 2022 at 18:37
  • @fixer1234 Great, thanks for the update. I'm glad it's like that, because that's a lot more intuitive (albeit potentially slightly misleading).
    – Joachim ♦
    Commented May 14, 2022 at 13:15
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Yes, the GSM (grams per square meter) unit is constant irrespective of paper type. It's the most common (scientific) way to compare different thicknesses of paper and ISO 536-2019 is the (current) international standard that defines how manufacturers are to measure that value. Unfortunately you have to pay for viewing the full content.

However, it only measures the grammage or weight of paper, not any other properties like density or rigidity.

Photo printing paper is a highly specialized paper for exactly one use-case. It's probably not made of common office paper, but of paper pulp that was preprocessed in a certain way. To achieve a very uniform thickness throughout the entire paper, the paper pulp was probably ground very fine. And it's also coated with a special substance for printing. All that influences the density of the finished paper.

Art paper is also a specialized paper, but for a different use-case, requiring different properties. The raw material (usually wood chips) may not have been ground down to the same smooth pulp as in the photo paper, giving the art paper a less uniform thickness, but more rigidity and a lower density, because it traps tiny air bubbles inside the paper. In addition to that, art paper is usually acid free, which rules out certain processing techniques of the paper pulp like acid baths.

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  • So theoretically they should have same weight.
    – Vikas
    Commented May 5, 2022 at 18:40
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    @Vikas If the packaging says they have the same weight, then they should have the same weight, even when they differ in other properties. You could put 10 or 20 pieces of each onto a kitchen scale and see for yourself.
    – Elmy ♦
    Commented May 5, 2022 at 19:36
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    @Vikas: They should have the same weight (per area). They probably won't have the same thickness or rigidity or other material properties. Just like a pound of lead and a pound of feathers won't have the same volume, or feel the same if you kick them or drop them on your toes.
    – Ilmari Karonen
    Commented May 8, 2022 at 13:42
  • @IlmariKaronen Hmm you are right.
    – Vikas
    Commented May 8, 2022 at 14:24

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