I was talking about certain studies
in the
past, and especially
this study (when opening PDF in Browser), that described the sound as "massless". However, the first two studies I've linked are quite old, and the last study I've linked didn't delve too much on "mass-less sound-waves" (quite strange, considering the last study I've linked was posted on 2022), compared to the other studies describing sound have "negative mass" and "negative gravity", so I guess the newer research caused a bit of a split in opinions.
But, considering there are more articles showing off the sound waves possessing negative mass and negative gravity, I guess you can consider them having "mass" (but negative) as more likely to be accurate in that sense. XD
Ah, my mistake. I might've mixed up Jogo having "sounds and explosives" attack, and Gojo blocking it showing he can block sound (when it's also possible that he might've dodged it with his Teleportation). XD
However, Gojo definitely appears to be able to block out heat with his Infinity at least. In multiple occasions, when Jogo sent fire-based and heat-based attacks towards Gojo, Gojo implied that Jogo's attacks was ineffective due to his Infinity.
If I recall correctly, I don't think heat itself has mass
(Unless there are newer peer-reviewed scientific studies that suggests that heat also has mass as well).
If it turns out heat doesn't have mass (and I'm pretty sure heat doesn't have shape either), then I guess that's the best feat "massless" object/attack Gojo has blocked with his Infinity?