We are shifting over from our known type of caps to the new ones with a plug and dosing system. This way you can measure our liquid concentrates more easily. The security plug has a second function as a dosing system and remains on the bottle. No fumbling in getting it off. We prefer plugs over welded seals because we encountered oxidation problems with our sealed bottles in the past. Plugs seal better and in case that developer crystalizes between plug and the cap it almost cannot fall back into the bottle through the little hole. Oxidized and crystalized old developer shortens the shelve life of your concentrate severely! ADOX Chemistry is filled into transparent bottles and caps so you can visually inspect your concentrates prior to usage. The transparent cap shows spots so you know when to clean it. ADOX liquid concentrates are fitted with a childproof cap for safety reasons.