Quilters argue about pressing the way other hobbies argue about brands. One camp presses every seam allowance to one side, the way their grandmother did; the other presses everything open, the way a garment sewist would. I've done whole quilts both ways, and the honest answer is that neither camp is simply right — the two methods solve different problems, and the best quilts I've made use both, chosen seam by seam. What follows is the actual tradeoff, without the tribal loyalty.
First, pressing is not ironing
Whichever direction you choose, the motion matters as much as the choice. Pressing means setting the iron down on the seam, letting heat and weight do the work, and lifting it straight up. Ironing — sliding the iron back and forth under pressure — is for shirts. A freshly sewn seam, especially anything near the bias, will stretch under a sliding iron before you ever notice it happening, and a stretched seam stays stretched. Every argument below assumes you're pressing; a slid-around seam allowance is distorted regardless of which way it points.
What pressing to the side buys you
Pressing both seam allowances to one side — traditionally toward the darker fabric, so the allowance doesn't shadow through the light one — has two real advantages. The first is nesting: when two side-pressed seams meet at an intersection and their allowances point in opposite directions, they butt up against each other and physically lock in place as they feed under the needle. That little ridge-against-ridge click is the single most reliable way to get crisp matched intersections, and it works with minimal pinning. The second is durability. A side-pressed seam hides its stitching under a fold of fabric; the thread never sits exposed at the surface, and the seam bears stress across two layers of fabric rather than across the stitches alone. Side-pressing is also simply faster — one sweep of the iron per seam instead of coaxing two allowances apart with a fingertip ahead of the iron.
What pressing open buys you
Pressing the allowances open, one to each side, distributes bulk instead of stacking it. A side-pressed seam puts three layers of fabric on one side of the stitching line and one on the other; an open seam puts two layers on each side. On a simple four-patch you'll barely notice the difference. Where it becomes decisive is anywhere many seams converge: the center of a pinwheel, the middle of an eight-point star, any block where six or eight allowances would otherwise pile onto the same spot into a lump the iron cannot flatten. Open seams turn those lumps into something that lies flat, which also pays off later — a flat top quilts more evenly, whether by hand or machine, and open seams are noticeably kinder if you plan dense allover quilting. Longarm quilters often ask for open seams for exactly this reason.
The costs are the mirror image of the benefits. Open seams cannot nest — there's no ridge to lock against — so every matched intersection needs a pin, and often a fine one placed exactly through both seam lines. They're slower to press, since each allowance has to be opened and held as the iron arrives. And the stitching sits exposed at the bottom of the open valley: pull an open-pressed seam apart and you're looking directly at the thread. That's not a structural crisis in a quilt that gets normal use, but it changes what the seam can tolerate, which is why the stitch length section below isn't optional reading.
If you press open, shorten your stitch
A side-pressed seam lets you get away with the 2.5 mm default stitch most machines wake up with. An open-pressed seam shouldn't. Because the thread alone bridges the gap between the two allowances, a longer stitch leaves visible pinholes of daylight at the seam line under tension, and it gives any single stitch more room to work loose. When I know a seam will be pressed open I drop to 1.8–2.0 mm before sewing it. The shorter stitch also survives the seam ripper less gracefully, which is the honest downside — unpicking a 1.8 mm seam is slow, penitential work, so save open pressing for seams you're confident in. One more consequence: quilting in the ditch runs right along the seam line, and on an open seam the ditch is the exposed thread itself. Stitching through it repeatedly weakens the very stitches holding the seam, so if you press open, plan quilting that travels beside the seam rather than in it.
A directional plan for rows
Where side-pressing really earns its keep is row assembly, and it only works if you plan direction before you press anything. The rule is simple: press all the seams in row one to the left, all the seams in row two to the right, and keep alternating down the quilt. When neighboring rows meet, every intersection arrives with its allowances already pointing in opposite directions, and every seam nests without negotiation. I write the direction on a sticky note pinned to each row stack, because re-pressing a row that went the wrong way is never as crisp as pressing it correctly the first time — the original fold line lingers in the fabric like a bad habit. The long seams that join row to row are their own decision: toward the bottom of the quilt by tradition, or open if the row seams are already carrying a lot of bulk from piecing.
How I actually decide
My working default is to the side, because nesting saves me more grief than bulk causes. I switch to open in three situations: any block where four or more seams meet at one point, blocks with lots of pieced points where a side-pressed ridge would distort the surrounding fabric, and any top headed for dense quilting where flatness matters more than assembly convenience. Mixing methods within one quilt is completely fine — nobody inspects your seam allowances — as long as any two seams that must nest with each other are both pressed to the side. The plan matters more than the ideology.
When the pressing itself goes wrong
The most common pressing complaint I hear is intersections that stay lumpy even though the seams were "supposed to nest." Nine times out of ten, one seam flipped direction partway along its length — pressed left at one end and drifted right by the other — so the intersection arrives with both allowances on the same side. Check the wrong side before blaming your piecing: a twisted seam shows up instantly as a fold that changes sides. The fix is to re-press that section from the wrong side first, iron straight down, and if the old crease refuses to surrender, a shot of steam or a spritz of water followed by a dry press will usually erase the fabric's memory. The other frequent failure is open seams that won't stay open, sneaking back toward closed as you handle the block. That's under-pressing: open the seam fully with your fingers ahead of the iron, press from the wrong side until it lies dead flat, then flip and press again from the front. A wooden seam roller or a clapper — anything that holds the heat in the fabric while it cools — makes an open seam behave far better than a quick pass of the iron alone ever will.