No spray foam won't reduce shock. If you haven't split much wood, then the shock you experience is more likely the death grip on the handle. Upon impact you are the shock absorber. I find that the Fiskars 8lb IsoCore maul is the number one. The weight does the work and it's concave design superior at penetration. If it sets without splintering, then I drive it home with a sledge. I also use a Council Tool GSA 4lb and they just introduced a 5lb splitting axe that's a true Maine wedge profile. These are the best values in splitting tools I highly recommend, if you use them correctly. I split 3-4 cords every year for the wood stove. Technique matters.