Trim to Fit: What to Check Before You Cut

A great many insoles are sold slightly oversized with a printed guide, on the understanding that you will cut them down. It is a sensible approach, since footwear varies more than shoe size suggests, and it is also the step where most people go wrong.

Cutting is irreversible. Everything below is about the checks that come first.

Use the shoe, not the foot

The commonest error is trimming to match your foot. The insole has to fit the shoe.

Take the existing footbed out of the shoe, if it removes, and use that as your template. It is already the exact shape of the space you are filling, which is better information than any printed size guide.

If the original does not come out, trace the inside of the shoe rather than measuring your foot.

Take the old one out

Worth stating separately because it gets skipped. Leaving the original footbed in and adding a new insole on top raises your foot considerably, tightens the shoe across the instep, and changes how your heel sits.

An insole designed to be a replacement will not perform as a layer.

Cut long, then trim again

The rule from every other trade that involves cutting applies here. Remove less than you think, put it in the shoe, check, and cut again.

Two or three passes takes an extra few minutes. One confident pass that goes too far means a new pair.

What to check between passes

Put the insole in and press it flat into the shoe. It should lie without buckling or riding up at the sides. A ridge along the edge means it is still too wide, and that ridge will be under your foot all shift.

Then put the shoe on. The heel should sit down properly rather than perched. Your toes should have the same room they had before.

Walk on it. Not around the room, but for a few minutes, because pressure points announce themselves under load rather than at rest.

Trim in stages and check under load. An insole that feels fine standing still can be entirely wrong after two hundred steps.

Different shoes, different cuts

The same insole shape rarely transfers cleanly between a work shoe, a clog and a trainer. The internal volumes differ, and the footbed shapes differ.

Which is the argument for a separate pair per shoe rather than moving one back and forth, and also a reason to trim each one to the specific shoe it will live in rather than to a compromise between two.

When not to trim at all

If you have been supplied with a device by a podiatrist, do not modify it. It has been made or selected for a purpose and altering it changes what it does.