A square-inspired design for kitchen shelves

This design for kitchen shelves is (as I'm sure you will have noticed) based on the pattern known as the Fibonacci Golden Spiral...

What is the best material for bookshelves?

Wood:

Red deal (higher quality smaller boards) or white deal (bigger pieces) - this kind of "softwood" is strong and long but because of inconsistencies and knots the surface often needs quite a bit of preparation, so to end up with a presentable finish it usually needs to be planed and/or scraped and sanded, and then filled and sanded again before being painted.

It is rare for softwood boards to be perfectly straight in their raw state, or completely uniform in thickness. Over time they can dry and shrink a little. They can be coaxed into shape, however, and allowances can be made for shrinking.

"Hardwoods" such as oak and mahogany are usually denser & smoother. They cost much more, but they often look decorative and they are usually oiled or varnished/lacquered - but because the whole surface is visible, extra time & care is needed for the most accurate joinery.

with wood:

18mm thick shelves - require vertical supports maximum 700mm apart

25mm thick shelves - require vertical supports maximum 900mm apart

As far as the depth of wooden shelves is concerned, we are limited to the width of the available boards, unless boards are joined (typically with "biscuits").

Alternatively edge-laminated softwood boards (with limited length) are available - these are made of numerous chunks, glued together.

Other Wood-based Materials:

Furniture Board - made of small pieces of wood glued together like a patchwork quilt. Strong and smooth, not given to warping but expensive if knots are kept to a minimum. 

Plywood (not as smooth as MDF) - is made of layers of wood. There are many different types, some with hardwood veneer.

Block board (which has thicker pieces in the middle of a ply sandwich).

Chipboard (rough surface, bendy).

Laminated chipboard (e.g. contiboard): the surface is smooth and already white. Thinner varieties are not strong - shelves tend to sag under even a modest load, although kitchen furniture is often made of thicker laminated chipboard.

with laminated chipboard:

12mm thick shelves - require vertical supports maximum 300mm apart

all the above wood-based materials require veneer/trim on the edges and they have severe limitations when it comes to inserting screws.

Medium Density Fibreboard:

MDF is made of dust and glue. It has a smooth finish and deceptively sharp edges (I have found to my cost), but the inside is furry, in the types that are widely available. It has a certain superficial toughness, but as a shelf it is not as strong as wood. Strength can be built up by gluing boards on top of each other, and MDF can actually be very useful in conjunction with real wood in vertical components.

MDF doesn't warp or twist (unless it becomes damp), and the thickness and consistency are very uniform, which means that it can be machined with a greater degree of accuracy than most softwood.

It can be unpleasant to work with (because of the toxic dust) and it always needs veneer/trim on the edges. MDF is usually painted, as the bland colour isn't to everyone's taste, but it's amazing what a strip of oak lipping and a whipe of Danish oil can do.  

with MDF:

18mm thick shelves - require verticals supports maximum 500mm apart

25mm thick shelves- require vertical supports maximum 700mm apart

Other materials:

Toughened glass

Steel

Plumbing fittings

Plastic

Reclaimed materials, such as crates, old books, old pianos, old cars