Papers are traditionally described in weight to illustrate how heavy and how thick the paper is to touch. Naturally the same goes for photographic papers. The method that suppliers use to rate the weight of the paper is pretty simple. It is achieved by given the paper the weight per square metre or in short GSM (grams per square metre g/m²) to describe the paper matter density. Common belief is that the heavier the paper is, the better its quality is due to feeling thicker to touch.
This method is often misleading especially when talking about photo papers as opposed to plain copier paper. Photographic papers are specialised media that are available in different shapes and more to the point, they are created using different manufacturing technologies which on occasion make GSM weight irrelevant in determining the quality of the paper.
To start with, we have the matte coated paper and the cast coated paper (instant dry paper). These two combine a regular paper with an Inkjet coating receiving layer which is applied directly on the “naked” paper. In this case, the weight of these papers will indeed reflect the thickness. Meaning that a 160gsm paper will feel thinner than the 260gsm paper
However there is another type of photographic paper, the microporous or nanoporous coated paper that are becoming more and more popular. These papers are superior to the cast coated and matt coated paper for two important reasons:
1. The microporous coating has a better compatibility with all inks and will provide a better image with more sub tones and colours.
2. The paper has a totally different base material. It contains a pressed paper with a polyethylene thin coating on both sides to protect the paper from moist and give it stability. Naturally these papers will be heavier than they feel as they contain pressed paper and polymer coating which is heavier than paper though thinner.
So what we got here is a bit of confusion.
Individuals who have bought a 260gsm paper with cast coated technology or matt coated paper will get quite a heavy feel paper due to it thickness. On the other hand an equivalent 260gsm microporous paper with a PE (polyethylene) base will feel lighter due to the fact that it is thinner despite being of the same weight.
Due to this reason films are measured in calliper (thickness) and rated in microns. Photographic papers on the other hand still display the traditional weight scoring which will probably need to change very soon to reflect the correct description of the paper. Quality therefore can be attributed to the coating technology rather than to the weight of the paper in GSM.