Wood

If you look really closely at wood you'll find that it's not just one thing, but several things all put together, mostly cellulose, lignin, and hemicellulose. Cellulose you likely know as the fibers present in paper (it also constitutes 90% of cotton) which work as crystalline tension cables holding the tree up. Lignin works as a block of glue in which those fibers are held together and which resists compression so trees don't crush themselves. And finally hemicellulose is glue-glue which attaches the cellulose to lignin.

Given that the whole wood composite is essentially a container of containers, cellulose in a matrix of lignin holding pockets of water and nutrients, wrapped in bark, packed to resist various stresses, it makes sense that wood is a fundamental to packaging. Over a third of all hardwood produced in the US goes to making pallets (the largest single consumer of hardwood). Over a third of softwood goes towards making houses, aka people-containers. Wood even has air pockets like the wavy chambers in corrugated cardboard, which if you take them out by vacuum can turn it into "densified" wood which is much stronger. So blend it, puff it, shrink it, harden it, or extract all the gaps and fill 'em with resin to make a transparent wood glass replacement for extra thermally insulating window panes on account of the lil cellulose chambers. A final note on packaging: the fourth largest energy consumer globally is wood pulp and paper production, more and more of which have gone towards... cardboard. Also paper has standardized sizes, but different sizes are used in the US than Europe. Similarly wooden pallets come in several sizes based on the dimensions of intermodal shipping containers as well as local door frame widths. "Standard-ish, but varied" is pervasive in wood's story (except when it's not).

Speaking of, wood is orthotropic, meaning it has consistent yet distinct properties in three perpendicular directions: up and down the tree, straight out from the trunk's core, and tangent to the trunk as if you put your hand on it. These differences depend on the grain of the wood, its growth rings, differences between the wood in the middle of the tree which grew when it was young ("juvenile" wood more similar to branches) and the wood further out in the trunk which came later. The grain runs up and down the tree because that's how water and sugars move up from the ground and down from the leaves where they each come from, and the cells which cellulose encloses are responsible for transport like a network of tiny straws connected together playing telephone passing molecular messages. Going out from the core, growth rings often demonstrate the differences between earlywood and latewood, grown in spring and summer each year and having different densities (though in exceptional trees these are invisibly uniform).

Branches grow differently than the trunk, contain what is called "reaction wood", and depending on the tree species take one one of two forms: extra cellulose on the top of the branch acting as bridge suspension cables is called "tension wood" while extra lignin on the bottom of the branch is called "compression wood" and works like the underside arch of a bridge. Reaction wood is also to be found in the trunks of trees in extra windy climes. Neat. On a brief tangent, the third direction which goes around the tree is what you'll find patterning most wooden boards, referred to as "plain-sawn", because you can't make boards which only go through the middle of the tree ("quarter-sawn", in case you were shopping). Darn. The nonuniform grain (it usually looks like waves reaching from one end of the board towards the other) is also responsible for how the board can warp if it gets wet.

Though it's already a little bit wet. Wood has a very close relationship with water, and not just because it likes to float like a boat. Even "dry" wood contains water, anywhere 6-20%, and will lose and gain water in proportion to its environment, making it "hygroscopic". Some woods before being dried are mostly water, like balsa which is basically a giant sponge (part of why it's so light once dry). Juicy. About six percent of world energy consumption, measured in exajoules (a billion billion joules), goes towards paper manufacture (IEA). You read that correctly: one out of every sixteen kilowatt hours consumed on the planet is used to make paper. In the United States, paper production uses 20% as much energy as all residential energy consumption combined. Separating water out is the most energy intensive part. This is also why softwoods like fir and pine are more popular than poplar: they're much cheaper to dry due to more open pores.

Wood's tiny pores are now being investigated for the very same purpose of separating water and reducing energy costs, namely by removing salt via solar steam generation. Wood coated with nanometals and half-submerged in saltwater absorbs hot on top from the sunlight and excites water moving through the nature-made cellulose nano-straws into steam for collection as freshwater. So throw a fancy log on that salty puddle and start your own solar-powered desalination plant.
Less futuristic but comparably more widespread is the advent of wood composite materials. The funnest is called glulam, but the most serious seems to be cross-laminated timber (CLT), popularized in 1994 in a Ph.D. thesis which you can still read online with the help of Google translate to extract the meanings from the matrix of German they're suspended in. (It even has its own search engine, just check out masstimberdatabase.umn.edu) Just as lignin suspends cellulose, CLT is formed by boards acting as big-ass fibers glued together in alternating directions to make panels with alternating layers pointing up-down and side-side. Remember the orthotropic material bit from earlier? By varying the direction CLT layers are alternately strong in multiple directions. Its advent in the 90's predated the changes to the International Building Code, later spurring the creation of a ICC Ad Hoc Committee on Tall Wood Buildings which have been defining the standards for making… tall wood buildings. These even have a cute name: plyscrapers. To date these buildings have been made over 25 stories tall, the current record holder at 284 feet is in Milwaukee, a mere 81.4 miles from the Forest Products Lab in Madison. One might say it's a growing market.

If you were wondering what fire safety regulations look like in something like that, you're not alone! The ICC cites a study done at the FPL in Madison in which they built a mock house with CLT, decked it out with IKEA furniture, and set it on fire by igniting cotton gauze and paper towels tucked inside of a kitchen cabinet. Tax dollars at work conducting hot research. Though they could have printed and used extra dollar bills for fun. They are, after all, mostly cellulose. Like the cotton gauze, paper towels, and wooden structure they were inside of.

Finally, a list of fun facts: The mountain pine beetle (the biggest pest affecting lumber production) is the second beetle to have its genome sequenced (after one which eats... wheat), there's a company genetically engineering poplars to photosynthesize more efficiently as a form of carbon capture, cellulose is birefringent (optically cool), there are currently 84 experimental forests and ranges managed by the US Forest Service, the botanical publication naming the substance lignin ("lignum" is Latin for wood) was also the first to use the word "taxonomy", the discoverer of cellulose also discovered the first enzyme (diastase) five years prior, and wood can be welded by heating it up without oxygen and melting it without burning so that the liquid interface attaching pieces makes a bond stronger than wood glue.

Unrelated to trees or the substance, "wood" used to mean "violently insane", which seems like a great replacement for the increasingly domesticated use of "wild" as extreme modifier. So when you tell your friends about this essay, you can reclaim the word for hip jargon by saying: it's pretty wood.