Non-Moldable Tray Bleaching Systems are not very effective and usually contain weaker concentrations of the active whitening agent. In some cases they do not use professional ingredients at all. Many of these system utilize a single dual-arch mouthpiece that will not allow you to talk, drink or breath properly when using.  These bleaching trays are also usually made from inferior plastics or foam and can cause uneven whitening (or striping) of the teeth.