Pressing Seams Open or to the Side: How to Decide

Both camps are right, which is why this argument never ends. Pressing seams open gives you a flatter quilt top and half the bulk at busy intersections. Pressing to the side gives you a stronger seam, intersections that lock together, and a quilt that stands up better to being machine quilted.

The useful question is not which is better. It is which of those four things your current block actually needs — and that changes from block to block within the same quilt.

What each one is physically doing

Press a seam to the side and both seam allowances fold together in one direction. The stitching line ends up covered by fabric, and the two allowances behave as a single unit — stiffer than the surrounding cloth, and slightly proud of it.

Press a seam open and the allowances split, one to each side. The stitching line is exposed on the back, the seam lies almost perfectly flat, and the bulk is spread across twice the width.

Everything below follows from those two facts.

The bulk arithmetic, which is more dramatic than people expect

Take an eight-pointed star — eight pieces meeting at a single center point.

Press every seam to the side and each of those eight seams contributes two layers of allowance to the center, all stacked in the same place. That is sixteen layers of fabric under the needle at one point, plus the pieces themselves.

Press them open and each seam contributes one layer to each side of its stitching line, so the same fabric is distributed around the center rather than piled into it. The high point is roughly half what it was.

Sixteen layers versus eight is not a subtle difference. It is the difference between a center that presses flat and a center with a visible lump that no amount of steam will resolve — and, on a domestic machine, the difference between quilting over it cleanly and breaking a needle. This is why open pressing is close to mandatory on Lone Star, Mariner's Compass, and anything else that converges many seams on one point.

Nesting, which is the entire case for pressing to the side

When two rows of blocks meet, their seam allowances have to cross. Press them to the side — and crucially, press adjacent rows in opposite directions — and the two allowances butt up against each other from either side of the seam. They physically lock. You can feel them click together as you align the rows, and once locked they cannot slide.

That mechanical registration is worth a great deal. It is what makes matched intersections achievable without pinning every single one, and it is why traditional piecing conventions specify pressing directions block by block. Open seams have nothing to nest with, so every intersection has to be pinned and held.

If you press open, budget the pins. If you press to the side, plan your directions before you start rather than discovering halfway through a row that two adjacent blocks both went the same way.

The argument most beginner guides leave out

Here is the one that matters for quilts that will be used and washed.

In a side-pressed seam, the stitching line is protected — it sits underneath the folded allowances, with fabric over it. In an open seam, the stitching line is exposed at the surface of the seam, and the only thing bridging the gap between the two pieces of fabric is thread.

That has two consequences. First, when a quilting stitch happens to land along an open seam line, the quilting needle can pierce the piecing thread itself rather than fabric, and repeated washing works at that point. Second, an open seam has no fabric reserve to take strain — all the load goes into the thread.

In practice this is a real but manageable risk, and it scales with use. A wall hanging will never notice. A quilt that lives on a child's bed and gets washed weekly will. If you press open on a quilt destined for hard use, shorten your piecing stitch a little — around 2.0mm rather than 2.5mm — so there is more thread holding the seam, and choose a strong fine thread. Our thread weights guide covers what to piece with.

Shadowing, and why "press toward the dark" exists

A side-pressed seam puts two layers of allowance behind one of the two fabrics. If those allowances are dark and the fabric they sit behind is light, they show through as a dark line — shadowing. Hence the old rule: press toward the darker fabric, so the dark allowance hides behind dark cloth.

Open pressing sidesteps the problem entirely, because each allowance sits behind its own fabric. On a high-contrast quilt — a red-and-white, or anything with a genuinely white background — that is a real argument for open, and it is the one that most often overrides the nesting advantage.

The decision, in one table

And the answer most experienced quilters actually land on: both, within the same quilt. Press to the side by default, and press open at the specific intersections where bulk becomes a problem. There is no rule requiring consistency across a whole top, and treating it as a per-seam decision rather than a philosophical position produces better quilts than either purist approach.

Doing each one properly

Both start the same way. Press the seam flat as it was sewn, closed, for a couple of seconds before opening it. This sets the stitches into the fabric and makes whichever press comes next noticeably sharper. It feels like a wasted step and it is the step.

To the side: open the pieces from the right side and press the seam over with the tip of the iron, working along the seam. Pressing from the right side is what prevents the small fold at the base of the seam — a pleat that steals width and shows as a fine ridge.

Open: finger-press or use a wooden pressing tool to open the allowances first, then set the iron down. Trying to open a seam with the iron alone tends to drag one side over and produce a seam that is open in some places and not others.

In both cases: press, do not iron. Set the iron down, lift, move, repeat. The sliding motion that is correct for a shirt is what distorts a pieced seam and stretches bias edges permanently — our guide to pressing vs ironing covers the technique and the tools in full.

A note on steam

Steam gives you a crisper press and it also makes fabric more willing to move — which cuts both ways. On a straight-grain seam, steam is your friend. On anything with a bias edge, steam plus pressure plus any sideways motion will stretch the piece and you will not get it back.

The common compromise is a dry iron for anything with bias in it, and steam for straight-grain seams and final pressing of the finished top. If you press a lot — and quilters do — a proper steam system holds temperature and steam volume far more consistently than a household iron, which our irons and steam systems guide goes into.

Quick answers

Does pressing open affect my seam allowance width?

Slightly, and in your favor. A side-pressed seam leaves the fold standing marginally proud, which consumes a fraction more width than an open seam does. It is a small effect, but it is one of the variables in why blocks finish undersized — covered properly in the scant quarter-inch seam.

What do longarm quilters prefer?

Ask yours — opinions genuinely differ. Most care far more about a top that is flat and square than about which way the seams went, and a top pressed carefully either way loads better than one pressed carelessly.

Should I press seams open on batiks?

At busy intersections, usually yes. A dense weave makes every layer of bulk count for more, and batiks press beautifully flat when opened. More on how batiks differ in sewing with batiks.

When do I press during chain piecing?

After clipping the chain apart, not before. Chain piecing is a batching technique — sew all the units, clip, then press them all in one pass at the board. Our chain piecing tutorial covers the workflow.

What about binding seams?

Open, without exception. Binding joins are cut on the diagonal specifically to spread bulk, and pressing them open is the second half of that job — see the binding guide.

Pressing is one of the few places where better equipment produces visibly better work: browse irons and steam systems, cutting and ironing mats, and sewing tools and accessories. If you are working through a first quilt, Your First Quilt puts pressing in sequence with everything else.