The purpose of this study is to compare the effects generated by the application of three different packs on the flexibility of the lower back of sedentary students. Method: Three sessions of 15 minutes of superficial heat through a hot pack (moist heat pack-MHP, seed pack-SP or gel pack-GP) were applied on the lower back. Pack and lower back temperatures and erythema were registered every 5 minutes. Schober test was performed before first session and after the third session.