Photo Papers are a general description for a variety of different inkjet papers, differing in their quality, type of coating, finish, weight, base paper etc. These factors affect the print quality of the photographs and are important to understand.
Weight: The weight of photo paper is measured by GSM (grammes per square meter). The weight is not necessarily indicative of the image quality as this is dictated more on the type of inkjet coating applied on the paper. The image quality depends on the coating; the print receiving layer, and by the type of the base paper onto which the coating is applied.
Calliper: Relates to the thickness of the paper, which is not necessarily always related to the weight of the paper. Some papers may be thicker and feel stiff, but will be lighter than some papers which feel thinner. The main reason for it is the two types of base papers used in photo papers:
1. PE Base Paper – This is the higher end base paper. This paper is amalgamation of normal paper pressed between two layers of polyethylene on both sides. This makes the paper heavier due to the polyethylene but not necessarily that thick. The benefit is that this paper is more stable and does not absorb humidity. Also it does not permit any ink that comes through the inkjet coating to penetrate to the paper and cause cockling (waves on the paper cause by over inking). The polyethylene layer acts as a barrier to protect the base paper, ensuring it stays flat at all times. The PE base paper is then coated on one side with an inkjet receiving layer which is the side you would print on.
2. Normal Base Paper – Is an ordinary paper which may come in different qualities, but would not have any barrier coating before the inkjet receiving layer (the coating you print on) is applied. In case of over inking, excess ink will seep through the coating and will get into the base paper underneath.
Usually, PE based paper will feel lighter than normal base paper although it may be even heavier. So when comparing PE based photo papers and normal based papers, you have to consider that the PE paper feels lighter even when it is heavier.
The PE base photo papers are normally used for Microporous high end premium photo papers and the normal paper are used for Cast Coated Photo Papers. More about the two types of coating and the benefits of each type of photo paper, in the next chapter.
Further reading – Overview of Inkjet Paper Types