Insoles for Running Shoes: What Actually Changes When You Run

Most running shoes ship with a thin foam liner that lifts right out. That matters because a real support insole is built to replace it, not stack on top of it. Leaving the factory liner in place raises your foot too high, crowds the toe box, and changes how the shoe was meant to hold your heel.

The two running-oriented models we track both assume you will do this. Our records mark the Superfeet Run Cushion High Arch as needing the factory insole removed, and the Spenco Polysorb Cross Trainer as recommending it. Before you buy either, it is worth checking that your running shoe's liner actually lifts out, since a glued-in liner changes the math.

Running insoles tend to sit somewhere on a line between soft and cushioned at one end and firm and structured at the other, and the two examples we track land in different spots. The Spenco Polysorb Cross Trainer is the softer, more cushioned of the pair in our notes, built to work across low, medium, and high arches, which makes it a forgiving starting point if you are not sure what your foot wants.

The Superfeet Run Cushion High Arch sits a step firmer. Our records describe it as a balanced-firmness, plush-cushion build shaped specifically for a high arch, with a deep heel cup to hold the back of the foot in place stride after stride. If you already know you have a tall arch and you want the heel held rather than floated, that shape is the point.

There is no single winner here, because the two ends solve different problems. Softer feels better underfoot on easy miles; firmer holds its shape longer under repeated impact. If you are torn, our arch guide walks through how to read your own arch before you commit to one end of that line.

A running insole has to share the shoe with your foot, so its thickness is part of the fit. Both models we track record a forefoot around five millimeters in the specifications we cite, and both list a deep heel cup, which needs a little vertical room at the back of the shoe to sit correctly. Our notes flag both as suited to standard and roomy running shoes rather than tight, low-volume ones.

The practical read: if your running shoes already feel snug with the factory liner in, a deep-heeled support insole may feel like too much even after you pull that liner. In that case a lower-volume shoe, or a thinner insole, is the better path. Our three-quarter versus full-length guide covers one common way to reclaim room without giving up support.

Both running examples we track are trim-to-fit, meaning they are sold in bands that each cover a range of sizes, and you cut the front edge down to your shoe. Our catalog records the Superfeet Run Cushion in a men 2.5 to 13 and women 4.5 to 14 family, and the Spenco Cross Trainer in a men 4 to 15.5 and women 5 to 12.5 family, with the specific band you buy set by the child listing on Amazon.

The trimming routine is the same for both: pull the shoe's liner, trace its outline onto the new insole, and cut the front to match, since trim-to-fit designs park the sizing slack at the toe. If cutting-versus-not is new to you, our trim-to-fit versus exact-size guide lays out the whole decision.

One habit protects every running-insole purchase. Whichever model you choose, confirm the size label, the current price, and availability on the Amazon listing itself before you check out, because the size dropdown, the price, and the stock all change independently of anything we record. The size that arrives is decided by the specific child listing in your cart, not the product photo.

If you would rather answer a few questions than compare specs, our two-minute questionnaire asks about your shoes, your arch, and your size, then points you to catalog entries whose size labels we have already verified. Prefer to browse? The full catalog is open, running models and all.