User blog comment:Dryst97/Fire is Superior than magma/@comment-1826677-20100213145717

It seems counterinuitive at first but once you relize the internal logic of the logia devil fruits you understand how Akainu could harm Ace.

All logias function under the principle that when their primary state is not compromised they can let all attacks pass through the body of their user. For example: Crocodile can only let attacks through when he is dry and can be hit when he loses this dryness. For Enel the primary state is conductivity. That is why Luffy could hit him because he is nonconductive.

It has become clear that Ace's state is not heat but combustion, while Akainu's state is heat. It does not matter how hot Ace becomes (assuming his ability had the capability to burn without limits in the first place) because Akainu is already molten. While Akainu clearly could somehow dampen Ace's combustion which is why he got burned (which he apparently was capable of) and which is why Akainu's attacks did not pass through him (well technically the final blow did but not in the good way).