Smooth and plied
The baseline: two or more strands twisted together into a round, even yarn. It shows every stitch, which is what cables, lace and colorwork want, and it wears best. Most of the worsted and DK shelves are this — Malabrigo Rios, Brown Sheep Nature Spun, Plymouth Worsted Merino Superwash. Plymouth Davila is a plied merino with a "pearl" twist, a slightly beaded surface that still shows a stitch. The single-ply vs plied guide is the contrast with what follows.
Single-ply
One strand, lightly twisted: soft, lofty, warm, blooming into a faint fuzz after washing that blurs stitch definition and hides uneven tension. Malabrigo Worsted and Rasta, Lamb's Pride, Noro Kureyon and Silk Garden, Álafoss Lopi. For plain fabric, hats, cowls and anything to be felted.
Tweed
A mostly solid base with neps — small knots of contrasting fiber — spun in. The classic sweater and vest look; it hides a few stray stitches and loves cables and simple texture. Studio Donegal Soft Donegal and Darnie are the real Irish article; The Fibre Co Arranmore Light adds cashmere and silk; Juniper Moon Saxony is a cashmere tweed; Noro Madara a tweedy single; Elsebeth Lavold Silky Wool and Berroco Remix Light have a dry, tweedy hand without neps. The Donegal tweed guide has more.
Slub and thick-and-thin
A yarn whose thickness varies along its length on purpose, so the fabric has a rustic, uneven surface. Juniper Moon Bud and Bud Dappled are chunky cotton slubs for fast summer tops and home textiles; Zitron Form & Farbe is a super-bulky slubbed merino; Noro Haunui Silk has a gentle thick-and-thin. Keep the stitch pattern plain — the yarn is the texture.
Chainette and blown
A fine tube knit like a tiny i-cord, sometimes filled with loose fiber ("blown"), instead of a twisted strand. It is light for its thickness, does not bias, and makes the lightest sweaters: Juniper Moon Cumulus (cotton blown into a nylon mesh, half the weight of a plain cotton), Cotton+Merino, Berroco Wizard at chunky weight, and Schoppel El Linio, a linen tape with a chainette construction. The lightness is the point; the catch is that a tube can be split by a sharp needle tip.
Brushed and halo
A yarn brushed after spinning so loose fibers stand out from the core and make a soft cloud: mohair and suri alpaca are the two fibers that do it best. Blue Sky Brushed Suri and Prairie, Artyarns Silk Mohair Glitter and Mohair Ombre, Dream in Color Billy Kid Silk, Berroco Aerial and Schoppel Silky Cat are the lace-weight halos, knit alone for an airy wrap or held alongside another yarn to put a halo on a sweater. Lamb's Pride's 15% mohair gives a smaller halo in a worsted. Halos hide stitches and cannot be ripped back cleanly, so swatch before committing. The mohair shelf.
Marl and gradient
Two plies in different colors twisted together make a marl — a flecked, two-tone strand; a yarn dyed in long runs makes a gradient that fades along the ball. Zauberball Crazy does both at once, each ply carrying its own gradient; Starke 6 is the heavier version; HiKoo Concentric is a baby alpaca gradient in a 200 g cake; Amano Riti and Schoppel Reggae Ombre fade more slowly. The self-striping guide explains how the width of the piece changes what you see.
Felted singles
A single-ply lightly felted after spinning so it holds together and pills less: Schoppel Reggae and In-Silk. The surface is matte and slightly fuzzy, the yarn is soft and light, and it felts hard if you ask it to.
Heathers
Fibers of two or three colors blended before spinning, for a solid-looking yarn with depth when you look close. The most forgiving texture there is for a beginner's sweater: Blue Sky Woolstok, Brown Sheep's heathered shades of Nature Spun and Lamb's Pride, Ewe Ewe Heather's Heathers, Plymouth Roam.
Sheen and glitter
Silk, bamboo viscose and longwools reflect light: Blue Sky Metalico (alpaca and silk), Juniper Moon Findley (merino and silk), HiKoo Sueño (merino and bamboo), West Yorkshire Spinners Wensleydale, Plymouth Tussah Kissed. Artyarns Silk Mohair Glitter adds a thread of Lurex to a mohair halo for the one shawl in the drawer that sparkles.
What knitters are asking for now
Four textures come up at the counter more every year, and they are all on the shelves: blown and chainette yarns for sweaters that weigh nothing (Cumulus); tweed for the plain, well-made sweater that is back in fashion (Soft Donegal); a mohair-silk held with a merino for a soft, hazy sweater (Billy Kid Silk or Aerial with Rios); and speckled or kettle-dyed semi-solids on plain stockinette (Malabrigo, Dream in Color). The fifth, chunky single-ply for a weekend hat, never went away (Rasta, Lopi).