WE ANSWER: Worsted Wool vs Woolen Spun.

We at Ziptown will offer you some winter sweaters and lightwear tops produced from the 100% worsted lambswool. So, we decided to explain our customers what is the difference between the regular woolen spun and worsted spun. Classically speaking there are 2 types of yarn. 
Woolen spun, and Worsted Spun. Back in “Ye Goode Old Dayes” all spinners would process their own fleece (or have a small child, or hefty man do it for them; more on that later…) and then use one of 2 spinning types to produce 2 very different yarns. 

Why are they different?
Well it’s all a matter of different fibre preparations, and different spinning techniques.

We’ll start off with what the yarns feel like.
Woolen yarns contains lots of air, they’re light, fluffy, and will often have small ends of fibre poking out of the yarn structure. They’re incredibly elastic and bouncy.
Worsted yarns are smooth and dense, they tend to drape well and be much more lustrous. Many commercial yarns are spun in this way, particularly sock yarns.

Woolen spun is traditionally spun from carded rolags (this was the job small children carried out). It’s then spun with the twist entering the drafting zone in a long draw technique. Carding, and the rolling in to a rolag creates a spiral of wool fibres wrapping round the tube. You then spin using a long draw technique that maintains that rolled structure. The yarn isn’t smoothed, it’s simply stretched out like a piece of chewing gum, that traps lots of air in the yarn, and makes it very bouncey and elastic.

There are various form of long draw, some make more air filled yarns than others, but the one thing they have in common is that drafting backwards motion, allowing twist to enter the drafting zone. 
As a beginner it can require a bit of faith, we’re generally taught to spin using a short forward draw, where letting twist past our front pinching hand can make it very hard to draft. This method requires twist to be be present however, as it’s the twist in the drafting zone that controls the yarn thickness. Once you get going it’s very easy to make a surprisingly consistent yarn using this method, as the yarn thickness almost becomes self controlling. Twist naturally navigates to thinner points, and those parts won’t draft out further as they have enough twist to hold together. The thicker parts have less twist, and as you pull back they will become thinner, the twist travels in to them and the yarn becomes even.

Historically this yarn was spun on Great Wheels. These wheels existed long before wheels with treadles, and because one hand was required to turn the wheel you needed to do a  single handed drafting technique. They were an incredibly efficient way of producing a lot of yarn, very quickly. Long draw is still may favourite technique when I need a quick skein of yarn. 
Worsted Spun requires a very different fibre preparation, and spinning technique. While woolen spinning is all about trapping air, worsted does the exact opposite. 
Instead of carding the fibres they’re combed. Hairs are aligned to be parallel, instead of being rolled up to perpendicular to the direction of the yarn. Twist isn’t allowed in to the drafting zone, and a short forward draw is used (this is the most common technique most modern spinners use).

Combing was traditionally done on large heavy combs, and was done by men. These are actually a scaled down version of the historical combs, but having handled a pair I can tell you that they’re still seriously heavy to handle. As modern spinners we can now get some much smaller and lighter combs, but combing is still a real physical workout. No need to go to the gym if you do an hours wool combing!

The combing process removed all the shorter length hairs, leaving behind fibres of the same length, free from tangles. It does however produce a lot of waste fibres (though those can still be carded for a more textured yarn).
When spinning the fibres run along the length of the yarn, which makes it dense, and also makes the yarn seem more shiny. High end suits are worsted spun wool.
Here’s a diagram of the yarns in cross section, that shows the difference in how the individual hairs are arranged inside the yarns.
It also illustrates why woolen spun yarns have more yardage for any given weight. So much of their structure is actually trapped air, which makes them very warm.