Quick Answer: Buttoned, a blazer is a shape — it creates a defined waist and a triangular line, and it depends on the button sitting at the right height for your torso. Open, it is a frame — two vertical lines running the length of your body, which lengthen and narrow. Most blazers are drafted to work one way better than the other, and the lapel roll tells you which.

If your blazer only ever looks right one way, that is by design.

What actually changes between the two?

The garment’s function changes entirely, from shaping to framing.

Buttoned, the blazer is defining your waist. The button position becomes the narrowest point of the outfit, and everything above and below flares from it. This creates an hourglass or a V shape depending on the cut.

This means button height is critical. A single button at the natural waist is the most flattering position because it puts the definition where the body actually narrows. A button higher up creates definition above the waist, which reads as boxy.

Buttoned also requires the blazer to actually fit through the bust and waist. Any pulling, gaping, or horizontal drag lines are immediately visible. The buttoned version is far less forgiving of fit.

Open, the blazer is framing your body. The two front edges create long vertical lines running from the shoulder to the hem, and vertical lines lengthen and narrow. The body underneath shows between them, which is what creates the effect.

Open is far more forgiving. Fit through the bust and waist becomes almost irrelevant, since nothing is being closed. This is why the open blazer has become the dominant way to wear one and why so many current cuts assume it.

What you wear underneath matters far more when open. The visible strip down the center is now a significant part of the outfit, and a plain top is doing more work than it appears to.

The lapel behaves differently. Buttoned, the lapel rolls to the button and forms a defined V. Open, it lies flatter and frames the neckline. A blazer with a very long lapel roll is drafted to be worn open.

How do I tell which way a blazer is meant to be worn?

Four indicators, all visible on the hanger.

1. Where the button sits. A single button at the natural waist is drafted to be buttoned. A button sitting low, near the hip, is drafted to hang open — buttoning it would create definition in the wrong place.

2. The length of the lapel roll. A long, low lapel roll that opens most of the chest is an open blazer cut. A shorter roll finishing higher indicates it was drafted to close.

3. The shoulder. A structured, padded shoulder with a set in sleeve holds its shape open, because the structure supports the front edges. A soft, unstructured shoulder collapses when open and generally looks better closed.

4. How it hangs when open on the hanger. Open the blazer on the hanger and look at the front edges. If they hang straight and parallel, it works open. If they curl inward or flare outward, it was drafted to close.

What to do with what you own:

If it was drafted to close and does not fit closed: wear it open with a belt over the top, or have the waist let out if there is seam allowance. A blazer that pulls when buttoned should not be buttoned.

If it was drafted to hang open and looks shapeless: add definition underneath — a fitted top, a belt worn over the blazer, or a tucked shirt. The blazer is framing, so the frame needs something worth framing.

The universal rule for a two or three button blazer: the bottom button is never fastened. This is a construction convention — the garment is cut assuming it stays open — and fastening it distorts the drape at the hip.

5 Mistakes That Make a Blazer Look Wrong

1. Buttoning the bottom button. On any two or three button blazer, the bottom button is decorative. The garment is cut so the hem flares slightly below the last fastened button, and closing it pulls the hem tight and creates drag lines across the hip.

2. Wearing it open with nothing structured underneath. An open blazer is a frame, and a frame around a shapeless base emphasizes the shapelessness. A fitted top, a tucked shirt, or a belt gives it something to frame.

3. Sleeve length left as bought. A blazer sleeve should end at the wrist bone, and the majority are sold too long. This is the single most common blazer fit failure, it is the cheapest alteration available, and it makes the largest visible difference.

4. Ignoring the shoulder seam. If it sits down your arm, no other adjustment will make the blazer look right. The shoulder is the purchase decision and everything else is negotiable.

5. Wearing a summer weight blazer into autumn. A linen or unlined cotton blazer reads as out of season from September and provides no warmth. The seasonal signal is the fabric weight, not the color or cut, and it is more visible than people expect.

How does the blazer work through the season change?

It is the most useful garment in the transitional wardrobe, and it does three different jobs as the weeks pass.

Late August: the blazer as a light layer, worn open. Over a summer dress, a tee and jeans, or a tank and trousers. An unlined or half lined blazer in a mid weight fabric is exactly right, and worn open it adds structure without warmth.

September: the blazer as the main outer layer. This is its peak season. A wool blend blazer over a fine knit is the outfit that covers the widest range of the month’s conditions, and it works buttoned or open depending on the temperature.

October: the blazer moves under a coat. Check that your coat closes comfortably over your blazer — this is a fit problem discovered every year in the first cold week. A blazer with a soft shoulder layers under a coat far better than a heavily structured one.

Fabric shifts to make now:

Move from linen and unlined cotton to wool blend, flannel, or a heavier crepe. The fabric weight is the seasonal signal, and a summer weight blazer worn in October reads as wrong even if the color is autumnal.

Colors that read as current: chocolate, deep olive, charcoal, navy, and burgundy. Black and navy are permanent.

Buy now if you are buying. Blazer availability peaks from late August through September, and the neutral colors in standard sizes go first, following the same pattern as all outerwear.

Get the sleeves altered immediately. A blazer bought this month and altered this month is ready for the season, and tailors are quiet now and busy from October. The sleeve length is what separates a blazer that looks bought from one that looks fitted.

Check last year’s blazers for shoulder pilling from bag straps, and for the lining condition. A failing lining is repairable and worth doing before the season, since it is the part that wears out first.

FAQ: Blazer Questions, Answered

Should I button my blazer or not?

It depends on how the blazer was drafted. A single button at the natural waist with a shorter lapel roll is meant to close; a low button with a long lapel roll is meant to hang open. Open the blazer on a hanger — if the front edges hang straight and parallel, it works open.

Why does my blazer pull when I button it?

The front panels do not have enough width for your bust, which is a pattern issue rather than a size issue. Sizing up adds width everywhere including the shoulders, so the better answer is to wear it open, move the button if there is overlap, or have bust darts added.

What is the most important blazer alteration?

Sleeve length. It should end at the wrist bone, most blazers are sold too long, it is the cheapest alteration available, and it makes the largest visible difference of any single adjustment.

Can I fasten the bottom button on a two button blazer?

No. The garment is cut so the hem flares below the last fastened button, and closing the bottom one pulls the hem tight and creates drag lines across the hip. This is a construction convention, not a style preference.

TL;DR:

• Buttoned, a blazer is a shape that defines the waist; open, it is a frame of two vertical lines. They are different garments.
• Button position and lapel roll length tell you which way it was drafted to be worn — check it on the hanger.
• Never fasten the bottom button on a two or three button blazer; the hem is cut to flare below it.
• Move to wool blend weights now, buy while the neutral sizes are in stock, and get the sleeves shortened while tailors are quiet.

Open your blazer on a hanger and look at the front edges. Straight and parallel means it was made to be worn open.