Paper matter

In search of good quality paper for the Lexmark Optra R+ (a B/W laser printer, 1200 DPI by the spec) I inspected the papers that I currently have been using plus some new samples a bit more closely.  Below scanning electron microscope images shows the surfaces of some papers or printing media, please click on the thumbnails for the larger images. 
 

	DPI	dot width in micro-meter
The images are at x300 magnification with 60 degree tilt. They have a 100 micro-meter scale, conversion of some common DPI's into micro-meters is on the right for convenience.  (1" = 25400 micrometers)	300 600 720 1200 1440	84.7 42.3 35.3 21.2 17.6

Sample 1: Mfg. A normal 80g/m2 copier paper.	Sample 2: Mfg. A 100g/m2 high grade color copier paper, 400 DPI machine.
Sample 3: Mfg. B normal 100g/m2 copier paper.	Sample 4: Mfg. B 100g/m2 color copier paper.
Sample 5: Mfg. C 90g/m2 laser paper	Sample 6: Mfg. D Backfilm super glossy, (film for backlighting,  pint mirror image on the backside)
Sample 7: Mfg. E Glossy dye-sub media (paper, base), 300 DPI machine.	Sample 8: Mfg. F Glossy dye-sub media (vinyl base),  150 DPI machine.
Sample 9: Mfg. G 100g/m2 high quality paper	Sample 10: Mfg. G 120g/m2 high quality paper
Sample 11: Mfg. G 135g/m2 high quality paper

The smoothness of the surface clearly is not the only issue that determines the quality of the print, but obviously matters a lot. Printing e.g. 21 micro-meter dots (1200 DPI) on paper like the samples 1, 2, 3 4, 5, 9 10 and 11 simply can not provide best possible quality since the roughness of the paper is at the same range. 

I was a bit surprised to find out that there is only a quite small difference between an typical xerox copier papers and the so called high grade color copier papers.

Two Sides 

Firstly it is important to notice that the paper has two sides, the notable thing is that they are not equally smooth/coarse. Sometimes this is obvious, e.g. Tektronix dye-sub paper has their name on the back-side and with glossy papers only one of the sides is glossy. 

But even with a common xerox copy paper one of the sides is most often better than the other (holes among the fibers are filled more and it is less grainy). With some brands the better side is indicated with an arrow or such on the wrapping, other brands do not indicate it but the difference is there still.

Surface Smoothness

With papers (the traditional paper) there seems to be two roughness related issues, the larger one is produced by the fibers, their width seem to range from 10 to 30 micro-meter. This seems to be so with all the traditional papers, no matter what quality or how glossy they are, the fibers are always there.

Then among the fibers, there is some filler matter and holes. The filler matter produces much finer grain at one micrometer range.

The glossy appearance seems to be a function of the finer grain (not the  fibers grain). Very glossy paper does not have a lot of the finer grain it is found only on lesser glossy papers. Such a very fine grain possibly does not affect a lot  to the printing with 21 micro-meter or larger dots so the benefit of a glossy (traditional) paper is just that, it appears to be glossy, lighter.

Vinyl (or plastic) base printing media are all very smooth. These are very good for printing at high resolution but not all the lasers and dye-subs like them, they can jam the printer or even damage it.

So called finished papers (super glossy, photo quality) papers are also very smooth, similar to the vinyl base materials. They have the same problem too,  not all the lasers and dye-subs like them.

Thick is better?

Samples 9, 10 and 11 shows different thickness of the same brand name paper. For this brand the lighter paper seem to be smoothest so thickness does not guarantee better quality.