SIS (Soft Is Strong) is the debut extended play (EP) by girl group Katseye.

Katseye was formed through the reality show Dream Academy, hosted as a joint venture by Hybe Corporation and Geffen Records, to create a girl group that will be promoted primarily in the United States.

A group of photos in the "Soft" series feature the members wearing costumes related to their assigned Dream Charm symbols.

NME's Mika Chen gave the album four out of five stars, describing it as "a surprisingly cohesive release that largely captures [Katseye's] enormous potential", but criticizes the short length of the tracks in the album, which resulted in "a song [that] ends a little bit too early or the feeling that it was just one final chorus away from perfection".

[15] Billboard Philippines' Gabriel Saulog described the album as "an excellent (and empowering) display of the varying sounds within the landscape of pop music", dubbing it as reminiscent of the 2000s and 2010s-style pop music by artists such as Little Mix and Britney Spears, with a blend of "modern K-pop elements".