[Svenn]

Since the bottom half of the jacket is generally buttoned-up and doubled-up flat over itself, wouldn't it be true that canvassing and structure is less important there? In fact, wouldn't one not want canvassing there so as to reduce bulk? I feel like full-canvassing is more critical in single-breasteds especially when they're unbuttoned, but this is still a mysterious topic to me.

 

[Flanderian]

Since the bottom half of the jacket is generally buttoned-up and doubled-up flat over itself, wouldn't it be true that canvassing and structure is less important there? In fact, wouldn't one not want canvassing there so as to reduce bulk? I feel like full-canvassing is more critical in single-breasteds especially when they're unbuttoned, but this is still a mysterious topic to me.

This is a complex issue, and while I'm marginally ignorant concerning the detailed intricacies of tailoring, I suspect there is no yes/no answer to your question. Fully canvassed tailoring, as does fused tailoring, and so-called un-constructed tailoring, each come in many versions. For example, both fully canvased and fused construction actually use canvassing, and such canvassing comes in variety of thickness and stiffness. Added to that is the preference of the wearer as to how he structured he wishes his clothing to appear.

But as a generality, all things being equal (Which, of course, they never are.) full canvasing can achieve both better drape, and more shape. than an equivalent fully fused jacket. And rather than believe it's less significant on a DB, such advantage might be even more so, since a DB will cosset the chest to a degree that a SB really doesn't, which I would think should make both drape and shape even more important.

 

[Matt S]

Since the bottom half of the jacket is generally buttoned-up and doubled-up flat over itself, wouldn't it be true that canvassing and structure is less important there? In fact, wouldn't one not want canvassing there so as to reduce bulk? I feel like full-canvassing is more critical in single-breasteds especially when they're unbuttoned, but this is still a mysterious topic to me.

Canvas helps provide the shape of the jacket. That shape is equally important in both single-breasted and double-breasted. If the jacket isn't fully canvased, it won't necessarily be lighter. Half-canvas jackets tend to be slightly bulkier because you have a fully fused front plus the upper half of the front is canvased.

And as Flanderian said, canvases vary a lot.

 

[16412]

While there is very little shaping down there the canvas is a foundation for the cloth to rest upon to give a clean appearance.
Some overcoats don't have the canvas all the way to the bottom.

 

[SG_67]

The canvas layer doesn’t add bulk. Also, I’d argue that it’s just as necessary and essential to a double breasted jacket, perhaps even more important though someone with more technical knowledge may disagree, due to the more complex geometry and the need for proper drape.

 

[Peak and Pine]

Is full canvasing less important on double breasteds?

It's less important on everything.
With vintage suits I used to loosen the lining near the opening, peek and make a written note if there was canvas. Then I realized that if I had to do that, i. e., couldn't tell from the wearing, that it didn't matter. So my stuff is a mix* and they all wear similar.

*Even the cheapest jackets from the 50s, like my high school blazer from Robert Hall were full canvased. My current, prized and pricey, Italian-made Polo chalk stripe flannel suit isn't.