This beautiful jacket above, made by Napoli Su Misura, is a fine example of Neapolitan tailoring.
When talking about Neapolitan tailoring, the discussion will invariably lead to the most famous feature of a Neapolitan jacket - the soft shoulder. The soft shoulder is a Neapolitan specialty, but it is not in itself the sole criterion that defines a Neapolitan jacket - not all Neapolitan tailors use it, and certainly not all tailors who use it are Neapolitan.
If we refer to the diagram below, we can see that there are several other common design elements to a Neapolitan jacket aside from the soft shoulder (A). Neapolitan jackets are often made with larger arms (B), wider lapels (C), more open quarters (D), and are often shorter than their British counterparts (E).
The famous soft shoulder that Neapolitan jackets are renowned for are created through the use of minimal (and sometimes non-existent) padding and canvas interlining. By using less padding, Neapolitan tailors are able to create a garment with a natural shoulder that is softer, lighter and airier compared to the typical English jacket.
The minimal use of padding is not the only defining feature of a Neapolitan-style shoulder, as mentioned earlier, Neapolitan coats are often made with wider sleeves. These wide sleeves contribute to a visual cue that has become a telltale sign of Neapolitan tailoring - shirring in the sleevehead.
Shirring refers to the pleat-like folds at the seam where the sleeve joins the shoulder. In a Neapolitan coat, the upper sleeve is cut much larger than the armscye, and since there is more cloth on one side than the other, the fabric puckers and gathers.
A discussion from the London Lounge explains the rational for the dramatic size difference:
This is not done for aesthetics, although the devotees of the style certainly claim it is beautiful. To the unknowing eye, it looks sloppy, like a sign of inferior tailoring. But it most definitely is not. It is not to everyone’s taste, however, and de gustibus, as the saying goes. Anyway, it is done for comfort and freedom of movement. Classic Neapolitan coats have very small armholes, very close shoulders, and relatively lean bodies—more roomy than a Roman or Continental coat, but less than traditional Savile Row, and much less than what is typically made in America. The large upper sleeve combined with the tight armhole, draped chest, fullness over the blades, and soft front canvas give the arms a most free range of movement. The coat can be worn all day, in almost any circumstance. The heat might get to you, but you will be able to do whatever it is that you need to do without having to take off your coat. (Within reason.)
A term often used to describe Neapolitan tailoring is spalla camicia (Italian for “shirt shoulder”) and manica camicia (Italian for “shirt sleeve”), both of these terms refer to a particular method of attaching the sleeve of a jacket to the body - it must be noted that although spalla camicia is associated with Neapolitan tailoring, it by itself does not define a Neapolitan jacket.
Spalla camicia refers to the usage of shirt-making techniques to attach a sleeve to the body of the jacket, but before we talk about that, we must revert back to the basics and talk about seams.
The diagram above represents the seam on a jacket where the sleeve joins the shoulder. The shoulder is shown in red, the sleeve in green, and the stitch that joins the two pieces in black. As you can imagine, it is difficult to attach two pieces of cloth right at their edges; so some excess width (called a seam allowance) is used to join the two pieces of cloth together.
After the two pieces are joined together. The seam allowance must be manipulated and tucked away. One method is to press and fold the seam allowance back onto itself (a.k.a “Pressed Open”, or “Open Seam”):
A second method to manage the seam allowance is to tuck the allowance from both pieces down onto the sleeve (a.k.a “Pressed Close”, or “Closed Seam”):
"Regular" (non spalla camicia) jackets manage the seam allowances of the sleevehead via these two methods; the second method is slightly more elegant as the excess bulk pushes the sleevehead up, creating a "bump" similar to roping. The Italians call this con rollino (“with roll”).
With spalla camicia, the seam allowances are folded and tucked back onto the shoulder, like so:
This is the same method employed by shirtmakers to attach the sleeves of dress shirts; spalla camicia simply refers to the utilization of shirt-making techniques in jackets. By tucking the seam allowance against the shoulder and not against the sleeve, the jacket is allowed to follow the shape of the body and fall naturally.
Jacket photos from Napoli Su Misura
Comparison photos from Kenyatte
Technical details referenced from: