The simplest and cheapest way of making a shoe is by sticking the upper to the sole. And certainly glues have improved immensely over the years and today they are extraordinarily strong. However there are disadvantages and there are superior methods of shoe and boot construction in the form of goodyear welt and blake stitching.
Glued, alias cemented, shoes are certainly very flexible from day one but they aren’t designed to be successfully re-soled. So when the soles do wear through that tends to be the end of their life. However stick-on soles if done when there is still plenty of sole leather is a way around this. And certainly cemented shoes work well especially for women looking for a fashion shoe.
In 1856 Lyman Blake developed a stitching machine which allowed the sole to be stitched directly to the upper leather, hence blake stitching. The sole remains attached directly to the upper so the shoe remains fairly flexible and re-soles at least a couple of times are realistic. Blake stitching shoes work perfectly well in the Mediterranean climate where it doesn’t matter too much if the upper is very close to the sole and make for a lighter looking shoe. However for more inclement weather it is better for the upper to be a little further away from the ground.
The revolution in shoe construction, especially for northern climes, came in 1869 with Charles Goodyear’s development of the Goodyear welting process. This method continues to be used today and is generally considered to be a superior method to blake stitching for the following reasons. The upper leather is stitched to a strip of leather, called the welt, with stitches which are not visible from outside the shoe. The welt is then stitched to the sole. The void created by the welt is filled with compressed cork. The combination of the welt and the cork makes for a well supported shoe which can then mould to the wearer’s foot. The fact that the sole is stitched to a replaceable welt means that the soles may be replaced numerous times without degrading the upper.