We are at the end of siman 29, and will discuss a few points not mentioned by the Chayei Adam.
We began discussing bottle caps yesterday. Another type of cap is known as a flip-top cap, such as found on sports drinks, where a plastic connector is torn off to allow the cap to open and close. Opening such a cap is for sure a problem of makeh bepatish, and one should open it before Shabbos. If one forgot to open it before Shabbos, one can puncture a hole through the cap, such that it is no longer functional as a cap when it is opened.
Regarding opening a tissue box on Shabbos, it is assur to open the box on the perforations. This applies both to the outer cardboard cover, and the inner plastic. Since it is not fully opened, it is an issue of both korea and makeh bepatish. Opening the box on its side, by separating the flaps which are glued together, is also an issue of korea, as we have discussed. One can destroy the container and remove the tissues such that the container is unusable as a kli. Since one is not creating a kli, it is not an issue of korea, or at the very least, it is derabanan and muttar due to kavod habriyos. As we have learned, it is muttar to open a bag of cutlery or other food utensils as it is muttar to open food.
Summary
Removing a bottle cap on Shabbos is not an issue of korea. However, it is makeh bepatish and possibly mechateich, because one creates the cap into a kli. This applies both to ring caps and flip top caps.
One can avoid the issue by making a hole in the cap to demonstrate that it has no functionality as a kli. Either way, it is preferable to open all caps–especially metal caps–before Shabbos.
It is assur to open a tissue box on its perforations. One must destroy the box such that they demonstrate the box has no functionality as a kli.
