Leather
Genuine leather usually refers to bonded leather - essentially a mashup of pieces of leather squeezed together.
Full grain leather is the high quality leather - it is the top of the hide with no adjustments, and has a very unique look to it.
Top grain leather is the second highest quality. It is similar to full grain, but the very surface of the hide is removed for a uniform look, eliminating surface-level imperfections.
The treatment of top grain leather prevents it from developing a lot of patina.
Care
Regularly apply leather conditioner or mink oil. There are other leather-specific oils that may be used, since mink oil is not very environmentally sustainable. This keeps leather from drying out and cracking.
Saddle soap should be used to clean leather.
Wax polish should always be applied last when caring for leather. To shine the leather, use a horsehair brush and rub the wax polish in circular motions.
Vegan / Faux Leather
Vegan leather is marketed as a good alternative to real leather, but it's not very comparable at all. Vegan leather is essentially plastic. It is prone to breaking or wearing out more quickly than real leather. When vegan leather breaks, it invariably ends up in a landfill. In contrast, real leather lasts far longer, and if it wears out, it can be naturally decomposed. Environmentally, since cows are being killed for food anyways, it is not additionally harmful to make leather from those cows. If you still feel icky about buying real leather, a good option (or the best option!) is to find a pre-owned leather item that has been well cared-for.
The Goodyear Welt (GYW)
The GYW is a construction method to make your (leather) boots reparable.
The leather upper of the shoe houses an insole that rests on a corkbed.
The corkbed and leather upper and stitched to a thin, flat strip of leather (the welt) that wraps around the shoe.
The welt is then stiched onto the midsole and possibly through to the outsole.
When the shoe needs to be resoled, you would simply unstitch and restitch the outsole on without affecting the rest of the shoe.
The GYW is often faked to give the appearance of quality, and so a telltale sign of a real GYW is that the stitches on the top of the visible welt match visible stitches on the bottom of the outsole, and the stitches have a reasonable tension (not loose) to be holding the welt, midsole, and outsole together.
According to Reddit, the best brand for trying out a GYW without too an enormous monetary investment would be Thursday Boots.
Other alternatives to the GYW would be the Stitchdown or Blake Stitch.
Wool
Wool is sheep hairs. Kind of anti microbial?
Merino wool
The main appeal is a decent amount of warmness while being very thin.
Icelandic wool
Icelandic wool (lopi) is one of my favorites. It's a very scratchy wool, but it's water resistant.
The icelandic sheep evolved separately enough from the rest of the world to develop outer hairs that repel water, and inner hairs that are warm.
The resulting wool is extremely warm and weatherproof.
Unfortunately, it's insanely difficult to find icelandic sweaters (and other ready-to-wear clothing) in the US, and so it's not that crazy to buy some yarn and make it yourself.
I buy my yarn (lettlopi, alafosslopi, etc) from Wool and Company Fine Yarn, which also has free shipping with no minimum.
Thread ply
Harvesting wool
Cashmere
Relatively simple.
Long thin fibers with low std dev of length and diameter are ideal. Results in less pilling.
Top-of-line cashmere (usually above 1k USD) are combed from cashmere and pashmina goats, ideally from the neck area of a young adult goat.
Cheap cashmere (under 500 USD) is obtained by collecting the fibers from entirely shaving a goat.
There is little to no regulation on cashmere quality, and so within any price range, quality may vary wildly.
The inner coat of the goat is generally softer.
Source: this Redditor
Care
Conair Fabric Shaver is good for removing lint and pills.