General vacuum forming

hi wondering if anyone can help me I'm a big star wars toy and figure collector and got into custom figure building but wanted to card my figure on custom cards for my own collection. I have card templates but wanted to vac form my own blister bubbles, I have built a very small vac former that I think will do the job. I tried to use an old plastic bottle made from PET I put it in the oven but it seemed to shrink not sag.. Is this because I'm using the wrong plastic or is it because its been vac formed before or just something else? if your wondering why I'm trying to use plastic bottles its because 2 reasons I cant seem to source cheap clear plastic and my kids go through so much bottled water there's no harm in trying it for free
can anyone help me with this problems has anyone used plastic bottles with success or is there a reason why its not used that I don't know?
any help would be much appreciated
thank you

Hi

you need to use PVC sheet ..... and not too thick .. otherwise you will get heavy webs on the corners ...

You cannot use an old plastic bottle for vacuum forming for several reasons, the main ones being that vac forming plastic needs to be a flat sheet the size of your platen, and the other is that formed (or in the case of the plastic bottle you tried to use which is heat roto molded) plastic has already been 'used' or 'formed'...once that's done (and this is also true in the case of thermo forming plastics like ABS and HIPS) you cannot re-use it because the physical properties of the plastic have been permanently altered. You must use newly, unused virgin extruded plastic for vac forming (you also cannot re-use or re form thermo forming plastics....it can only be used once). Also, plastic bottles are made from a different type of plastic (even though it's PET based) made specifically for heat roto molding and cannot be used for vac forming...it's like trying to make orange juice from apples...two different things.
I would STRONGLY recommend going to the following forum posted below and doing more research before moving forward with vac forming. Good luck!
www.TK560.com :: View Forum - Vacuum Forming & General Stuff