Nowadays, not much, but originally roller hockey equip was made to vent, with lots of mesh and space for air to flow through (as roller didn't have the ice to cool down a player) Recently ice hockey equipment has been made with similar venting systems to cool down a player and because of the decreased weight without sacrificing strength.
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I think the difference is that Ice Hockey is played on ice with ice skates and in-line hockey is played on a flat surface with rollerblades.