Sauna blankets and online therapy: a new way to beat insomnia?

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: * 18 years or older * English-speaking * Willing to use birth control if assigned female sex at birth * Willing to receive study text messages during participation * Location to plug sauna blanket into regular wall outlet * Ability to lie in sauna blanket for 15 minutes * Ability to fit in the sauna blanket * Daily access to the internet via computer, smartphone, or tablet * Elevated insomnia symptoms as indexed by a score of 11 or greater on the Insomnia Severity Index (ISI) at two screening timepoints * Primary insomnia disorder (characterized by difficulty initiating sleep) as indexed by a positive diagnosis on the Structured Clinical Interview for DSM-5 Sleep Disorders (SCISD) Exclusion Criteria: * Night shift or swing shift worker * Current or planned routine body heating practices (e.g., saunas, hot tubs, long baths) within 4 hours before bed that are 10 minutes or more in duration (≥2x per week) * Pregnant or plans to become pregnant during the participation period * Traveling internationally between screening assessment and anticipated post-intervention assessment, or during anticipated post-follow-up assessment period (\~1 week) * Other diagnosed sleep disorders or suspected sleep disorders * Medical conditions that might increase the risk of passive body heating using an infrared sauna blanket * Medication use that might increase the risk of passive body heating using an infrared sauna blanket * Mental health disorder that may better explain insomnia, require priority treatment, or be exacerbated by time in bed restriction * Medical condition that may better explain insomnia, require priority treatment, or be exacerbated by time in bed restriction * Lifetime diagnosis of a bipolar disorder, psychosis, or other psychotic disorder * Current (past 3 months) major depressive disorder * Current (past 12 months) suicidality, alcohol use disorder, other substance use disorder (except mild cannabis use disorder), panic disorder, agoraphobia, social anxiety disorder, obsessive-compulsive disorder, attention-deficit/hyperactivity disorder, post-traumatic stress disorder, and eating disorders * If using medications for mental health treatment (e.g., antidepressant medication) must have been on a stable dose for prior 8 weeks * Currently receiving cognitive behavioral therapy for insomnia (CBT-I)