The thin, soft plastic trays provide sufficient comfort to allow teeth whitening while you sleep. Our sticky Hi-Intensity™ Competitive Strength Teeth Whitening Gel formula sticks to the DURABRITE™ Custom Fitted Teeth Whitening Tray and firmly holds it against your teeth to whiten. The formula is gentle enough to wear overnight. You can use the DURABRITE™ Custom Fitted Teeth Whitening Tray for 1 to 3 hours during the day or at night while you sleep. You should continue the Lab Direct™ Teeth Whitening Process for a complete and full curing which generally takes 12 days. However you should see up to 7 shades whiter after only 1 day. The Hi-Intensity™ Competitive Strength Teeth Whitening Gel really only works for up to 3 hours therefore sleeping in your trays will not cause over whitening. Do not eat or drink while wearing your DURABRITE™ Custom Fitted Teeth Whitening Trays.