The fundamental schism
in the photographic paper world is between fibre based papers (dearly
beloved of darkroom aficionados and fine art practitioners) and resin
coated (popular in the commercial domains).
Inkjet paper has two key components - a substrate layer (the paper itself) and an ink receptive coating.
Resin Coated Inkjet Papers
are the papers most people regard as 'photographic' because they're the
sorts of places your typical mini-lab use - these papers are made using
a layer of (usually low grade) wood pulp, over which a layer of
plastic is placed (usually polyethylene). This forms a barrier between
the paper substrate and the ink receptive coating that is placed on top
to the plastic (resin) layer. This use of a plastic layer makes for a
very commercial, ultra smooth appearance. It tends to strip the final
print of any of the paper's original character. Sometimes this
clinical, commercial look has benefits, but very often it can make for
a lifeless print.
Fibre Based Inkjet Papers
are made of a substrate (usually cotton rag fibres or high grade wood
pulp, see below) upon which an ink receptive coating is directly
placed. This means the character of the underlying paper tends to show
through the ink receptive layer, making for a final print where the
character of the paper adds to the expressive qualities of the print.
Further, because the ink receptive layer and paper substrate are in
direct contact, these papers can typically accept a higher ink load,
meaning stronger blacks and greater colour saturation can be achieved.
Baryta
is a word you'll often hear with respect to fibre based papers - this
was a layer used in traditional silver gelatin darkroom papers between
the paper base and the light receptive coating. This is, for many, the
holy grail of paper - these papers had a unique look and feel that many
regard as the pinnacle of photographic expression. Recent inkjet papers
have come very close to this
appearance.