Some of us have lumpy heads, lumpy enough to make a helmet uncomfortable and us less likely to wear one.

You can moderately thin and reshape the foam liner where your lump is with a ball peen hammer. While thinning the foam does reduce the helmet’s ultimate protection in that place, it also allows one to wear the thing in the first place.

Do not cut foam away. Dent it.

Some years ago, I asked David Thom at USC if he could test a helmet with a quarter-inch thickness of foam cut away in the impact area and make the same drop test with the thickness reduced the same amount with a hammer. He thought it was an interesting question and made the tests. I believe Dave made the normal DOT flat anvil drop.

The dented impact gave normal “g” number; the denting did not seem to matter. The cut foam drop gave a higher peak “g” number; not much higher but higher just the same.

So, if you need to make room for a lump, do it with a ball peen hammer and not a knife ;o)

Joe