Replacement Insoles

Many of my favorite shoe brands are gravitating to using open-cell, Ortholite insoles.  I can understand it as they have a great feel when first putting on a shoe, don't move about much and seem to last well.  In addition, brands seem to be gravitating towards thicker insoles; Inov-8 for example now uses a 6mm insole in most (all?) of its shoes.

A dry, Ortholite, 6mm Footbed

Unfortunately, these insoles are open-cell foam which means that they absorb water.  A lot of water.  A dry 6mm insole weights in at 25g in my size UK 8.5.  The same insole, soaked in water increases in weight to 121g.  Treading on the insole will start to pump this water out, but unless it leaves the shoe instantly it just sucks straight back into the insole again when unweighted. In practice, after a soaking and then running a short distance (100m) I have found that the weight gain of the insole alone is somewhere around 80-90g on average.

A wet, Ortholite, 6mm Footbed

Most shoe reviews discuss the weight of a shoe and cite small differences as being critical, and if you are running in wet areas then an Ortholite insole could be increasing the weight of your shoe by as much as 40% through water absorption.  In addition, this pumping of water in and out of the foam is costing you energy, and resulting in an unpleasant squelch.

A 6mm Neoprene Footbed

I'm a big fan of Inov-8 shoes but I don't like the additional weight or squelch with their insoles.  In searching for replacements I found very few that were thick enough and they were usually very expensive. To solve the problem, I have tested  EVA and Neoprene sheet which can be purchased on Amazon for less than the cost of a replacement insole.


Making the insole was quick and simple. I traced a line around the outside of the existing insole and then cut the insole out with scissors.  It took about 5 minutes to make a pair.

Results

EVA: Light (7g), stiffer and provides a bit more protection than either the original insole or the Neoprene.  It doesn't have much 'spring' to it, and feels like it could compress over time.  The EVA foam that I was able to get had no lining material, so it might benefit from a thin commercial footbed on top.

Neoprene: 18g, so lighter than the original footbed (25g).  The neoprene is 'floppy' but has more of a rubbery feel to it and you can definitely sense more 'spring' underfoot.  I don't expect this to compress much.  The neoprene deforms locally to provide more surface deformation or 'squish' - you can almost imagine it squeezing up between your toes and this provides a good slipper like softness when you first put the shoe on - personally I'm not a big fan of that type of feel but I know a lot of people are. The Neoprene that I got was lined on both sides - it might be better if you could find some lined on one side only.

Neither the Neoprene or the EVA absorbed any water.

What to use

The EVA might contribute a bit more protection, in effect adding thickness to the midsole, but I think that the EVA will work better with something to line it - either a thin off the shelf insole or perhaps a thin sheet of Neoprene.

I like the bounce of the neoprene and, for simplicity, I would probably go for that as a simple replacement of a thick Ortholite insole, unless I wanted to give a shoe a bit more protection.

I also liked the feel of the Neoprene under a stiffer insole - you still feel the bounce but without the squish (which I'm not a fan of personally).  I think that this could be my favorite combination and certainly, if I had a shoe which I was looking to take up some room in then a Neoprene layer under the existing footbed would be great.

I'm interested to try PVC and PU.  I suspect that PU, in particular, might be a little stiffer and could work well in combination with the Neoprene... watch this space.

It is worth noting that because these are foams, there could be fairly large differences in density and, because they were not bought from technical suppliers, I don't have those details, so your experience might vary.