Welding Plastic Bags

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Introduction: Welding Plastic Bags

Plastic bags can be welded together with a soldering iron. The resulting seam is strong and water resistant. This is a very useful technique for making kites.

Step 1: Tools

You need some oven paper and a soldering iron.
I use a soldering iron with a flat tip and temperature control.

Step 2: Stack Materials

Place the first piece of plastic on some oven paper and mark the place where you want to make the seam. Then place the other piece over the first one aligning it with the mark.
The plastic sheets are slippery and they like to escape. You can make them stick in place by wetting them just a bit.
Now place another piece of oven paper on top of the plastic. You should be able to see the markings through the paper. This is why it is a good idea to use light colors and avoid black plastic.

Step 3: Welding the Seam

With very little pressure on the soldering iron move it along the seam to melt the plastic sheets. It is important that you hold the tip so that the whole surface of the tip makes contact with the paper.
The right speed depends on the thickness of the plastic. Low density plastic is easier to weld than high density because HD is thinner.

Step 4: Done!

When you have finished the seam, inspect it and test it by tearing it apart.
After some practising you will know the right speed and presure for different materials.

Use your new skill for making kites or inflatable stuff or something!

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49 Discussions

I just tried the pencil gun & 2 sticks method on thick black polythene - the kind you use to line building foundations. It worked great. The sticks I used had chamfered edges so formed a small "V" and I used a roller (the kind you use for gluing veneer or drywall taping) to press the edges together. I formed a sleeve that held water without leeks first time out!

I am always surprised by the different uses on how to use welding. I would like to find a welding project for myself. I hope that I am able to find the best thing for myself. There are a lot of things to choose from.

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colin

12 years ago

This is a nice technique. What temperature are you using for your soldering iron? Also, what happens if you don't use the oven paper? Does it coat the soldering iron tip with nasty melted plastic?

4 replies

I have seamed plastic by putting two pieces together, between two very flat pieces of wood. Use portable torch to lightly melt the plastic. Stick the ends out around a quarter inch beyond the wood. The seam is a little thick. A portable plastic sealer, like those used for sealing snack bags might work as well.

Just used this method best one yet so easy and fast. You deserve a gold star. Dilwyn lammas. Also posted method

Do not try it without the oven paper if you are very close to a smoke alarm. You can clean the tip of your soldering iron by pushing it through a cardboard box a few times when it is still smoking :) The iron I use is not adjustable and I have never measured the temperature. If I need to be very careful I fold the oven paper double to reduce the temperature a little.

Melting point of LDPE is 248 deg. F, you don't need to go above that. I just melted a bunch of bags in a pot on my stove. Colin, yes the bags get goopy and if you continue to apply heat, burn and smoke. I don't recommend attempting to make liquid LDPE in your home kitchen. If you do, use the maximum of ventilation.

Hi. just tried the two pieces of wood with material sandwiched tightly in a workmate worked first time. Used very small gas pencil blowgun of Ebay 1,300c. Really strong join, shall use this meathod to make new roof for gazebo, BRILL. Thanks Dilwyn Lammas

It is posible to join transparent vinyl fabric using this technique?, can I use a circuit solder equipment?

Excellent, this was what I needed to apply a plastic liner for a storage unit but none were made for the unit so I made one myself using your instructions. Thank you so much for the info. The unit is now lined with plastic and water resistant. A few hits of silicone at the screw points and all done.

I once used freezer bag plastic, a reconfigured freezer bag sealer and waxed paper like this to make 2 long tubes for sled kite spars. I blew some air in, rolled the tube around a dowel to build up air pressure, pressed a straightedge down to contain the air and sealed it up on the unpressured side. I couldn't believe that I could stand on the tube without popping it ! The rest of the kite was lighter weight garbage bag plastic. The pressure was plenty enough to keep the sled kite in shape. It flew in very light breezes.
I made another sled by overlapping plastic from a walmart bag and sealing in 2 places for each spar, leaving a long narrow tube for inflating and rolling up around the dowel. It actually took very little pressure to keep the kite in shape. When I let the reel spin free, the kite went downwind nearly horizontally and shot upward as soon as I stopped letting line out. Some type of reuseable valve could make these saleable.

Just now finished an attempt at making some tubing, and its a good first try! I only used a cut section of one bag wrapped around a paper stick with a layer of parchment inbetween the plastic. So far, its like a fragile drinking straw with a bunch of small holes in it.

next time, im making it thicker and not applying as much heat. In this case for flexible tubing, possibly, too much heat will make it too stiff and hard.

i would think,that if you had a wood burning tool( they are bigger yes?) a thin thin metal cutting blade and some tinkering would allow you to place a roller into the gap at the tip of a wood tool.

Wow, this is awesome! Thanks so much for your instructable, this is really going to help when I build a garbage bag blimp!

In this context, I would think that "oven paper" would be the same as parchment paper. The difference is that parchment paper is coated with a thin layer of silicon and can withstand the heat of the oven.  Waxed paper would melt.

Suzanne in Orting, WA

an idea just popped! this can be used to extend 2 liter bottles, or can it? submarines any one? or 2 liter-bottle long boat, or better bottle rocket! This plastic welding technique will be perfect for building an inflatable tent that can stay inflated with a computer cooling fan and 9v battery.