This universal sealing clip is suitable for almost all soft materials such as film bags and balloons. The clamping force is distributed evenly to prevent damaging the material and seal across larger areas.
You can measure the thickness of the material with a pair of calipers and use that value for the gap. If your printer is well calibrated the value shouldn't need too much adjustment, if any at all.
It is designed not to have any sharp points but you may have to check the final print over and clean it up depending on your printer.
Ikea 60mm Clip: 40mm length, 4.5mm Studs, 1.1mm Gap.
Ikea 110mm Clip: 90mm length, 4.5mm Studs, 1.1mm Gap.
In case anyone is interested, the filament I use is made by Aurarum Australia.
Print without support.