heres one thing to rememmber if you are going to use a canaster mask when your done place the filters cans in a zip lock plactic bag.
so you can reuse them. if left open they will absorb particals from the open air and with in less then one month they will become use less and will need to be replace. also make sure that you cover both side of the filter can with a piece of duck tape befor you store them also kept track of the exposeture time when you use the filters there is a set amount of hrs. that they are good for... I use a full face hepa mask and a less expenctive stackable can. mask both are very good... please do not use a paper or cotton mask THEY DONT WORK FOR FUMES...