After releasing "Holy Roller" and "Constance" as singles in the latter half of 2020, Spiritbox relocated to Joshua Tree, California, in early 2021 and completed songwriting for the album.

Eternal Blue includes several heavy metal genres and subgenres, and electronic elements, and LaPlante used both screamed and clean vocals on the album.

[8] As Spiritbox, LaPlante and Stringer released the single "The Beauty of Suffering", which was followed by a seven-song, self-titled debut extended play (EP) on October 27, 2017.

[19] The band reconvened in Joshua Tree, California, to work in "their own bubble", which allowed them to continue writing songs and revise existing material together during the pandemic.

[16] Braunstein recorded it with the band in complete isolation at an Airbnb rental house located on a 20-acre (8.1 ha) desert property in Joshua Tree,[16][20] referred to as the Old Heard Ranch.

[36] The group said they were inspired by the 1980s pop music scene, Nine Inch Nails, and early post-punk bands such as The Cure during the album's production.

style of music" in his previous bands, and made a concerted effort with Spiritbox to diversify his approach into a more mature one which yielded more memorable tracks rather than a small portion of a song, whether atmospheric or heavy in nature.

[20] The album and its title track take their name from EternalBlue, a computer exploit the United States' National Security Agency (NSA) developed.

The song creates a dramatic atmosphere LaPlante envisioned as ideal for a band's entrance to a live show, and in the same way was chosen to open the album.

[38] "Hurt You", which was also written in early 2020 prior to the COVID-19 pandemic, is a nu metal song that explores how it feels to stay in a doomed romantic relationship that is riddled with "toxic co-dependency".

[38] LaPlante described "Yellowjacket" as "inhumanly heavy"; throughout the song, her vocal performance alternates between her "scariest" screams and normal speech.

LaPlante initially did not want any guests to appear on the album, citing travel difficulties during the pandemic and a desire to prove herself as a capable vocalist without outside exposure.

[40] According to LaPlante, "The Summit" is an attempt to bend musical genres in a way "that doesn't make sense"; she found defining the song as heavy metal was difficult.

[23] "Secret Garden", which was written in mid-2019,[38] showcases what LaPlante called the "fluidity that is inherent in heavy music" and the diverse metal styles of Spiritbox.

[38] In "Holy Roller", LaPlante takes the role of the Christian Devil, speaking internally to the listener as a sort of personified evil.

[2] Kill Your Stereo journalist Alex Sievers described it as the band's heaviest song, "far darker and more violent" than any of their previous material.

[44] "We Live In a Strange World" was also written before the COVID-19 pandemic; the lyrics serve as LaPlante's anxiety about Spiritbox's growing recognition and her fear of failure.

The song includes "breathy vocals" and melodies that mixing guitars with electronic instrumentation, contrasting with harsher parts and a breakdown.

[45] The closing track, "Constance", takes an ethereal approach to metal one critic described as "the polar opposite" of "Holy Roller".

[51] Although he had never met Spiritbox, Shinedown singer Brent Smith offered them $10,000 to cover costs, concerned that the band would collapse from the financial hardship.

[51][52] With the exception of an appearance on the Coheed and Cambria-headlined S.S. Neverender cruise in October 2021,[53] Spiritbox did not begin live performances in support of the album until 2022, when they were a special guest on Underoath's Voyeurist tour in February and March, joining Bad Omens and Stray from the Path.

"Eternal Blue" and "Halcyon" were highlighted by Owen Morawitz at New Noise Magazine for their songwriting and musical versatility, which he cited as reasons the album could appeal even to the most skeptical listeners.

[24] Outburn's Nathan Katsiaficas also praised "Halcyon" for its turn from light to heavy, which he felt "encompasses the variety of dynamics" showcased on Eternal Blue.

Calling the record a "modern metal masterpiece", he highlighted its songwriting and musicianship as key elements that make it an exciting listen from start to finish.

reviewer Steve Beebee noted the contrast of "dreamlike soundscapes" on "Secret Garden" and "The Summit" with the heaviness of "Silk in the Strings" and "Holy Roller".

[25] Comparing it to the works of Tesseract, Deftones, and Meshuggah, AllMusic's Neil Z. Yeung said fans of these bands would particularly appreciate tracks like "Circle With Me" and "Eternal Blue".

The contrast between the brutality of "Holy Roller" and the cleaner, more atmospheric nature of "Constance" stood out to him, and he singled out "Secret Garden" as among the album's strongest tracks, particularly for its hook.

[80] Metal Hammer's Dannii Leivers noted that, while Spiritbox's combination of heavier and gentler sounds was not a new concept, the material on Eternal Blue carries an emotional tone that improves its appeal.