Introduction: Plastic Smithing: How to Make Your Own HDPE Plastic Anything (DIY Plastic Lumber)

Picture of Plastic Smithing: How to Make Your Own HDPE Plastic Anything (DIY Plastic Lumber)

How to make really good hard plastic while reusing and recycling plastic bags at home! Via this method, you can make ANYTHING you want to, out of hard, lightweight, real plastic that's astoundingly durable. It comes out very similar in texture to recycled plastic lumber.

best of all, this method involves no fumes!

I'm gonna show you how to make plastic wheels for your robot!

I first heard about stewing plastic bags to make new things from Dave Huebsch's book " Village Assignment " about interesting adventures had while running a charity/NGO (" Common Hope ") in Guatemala. He, amazingly, repaired the bottom weight-carrying main bearing of a washing machine with a big plastic disc made of stewed plastic bags, which actually was such a good stand-in replacement that it held up for several years. (and here are some more Guatemalan Handy Tricks)

I had to try it right away, and the first couple times I just burnt plastic, until I came up with this method.

By the end of this, you'll be able to make yourself a knife sheath, mold around your shoes and make DIY hard-toe sneakers, wheels, bearings, bushings, or any kind of plastic part! Take pictures and post them in the comments!

Step 1: Materials

Picture of Materials

Collect all the plastic bags you can get, they shrink down a lot.
Shredding them will make your final texture finer.

Use an old pot that you aren't going to use for food any more, or get one secondhand for really cheap at a thrift store.

Find a stick or something else you can use for a spatula.

I liked the clothespin a lot because I could pick things up as well as stir.

Oh, and oil! (I used canola because it was right there next to my stove. If you're, for example, making a bearing you can impregnate it with your personal favorite grease.)

So grab your favorite oil, here's why:

Plastic bags are made of LDPE (low density polyethylene) which melts at 248 F.

I got the temperature wrong and tried doing this in a homemade double boiler filled with water (to regulate the temperature to water's boiling point), which, of course, just made hot plastic bags.

After the double-boiler mistake I re-read the LDPE melt-point and discovered my folly! So I came up with melting them in oil.

Cooking oil boils around 350, which is far too hot for plastic, and which you don't want anyway (splashing boiling oil = no fun unless you're a hun), so I keep it to a nice low-viscosity canola oil heat and things work just fine.

If you wanted a smooth, non-oily finished surface, consider using wax instead.

ALSO: oil is not required per se --
if you had a constant temperature hot surface that you could guarantee to keep down around the melting point, you could do this just fine with no oil or wax!

Step 2: Add Oil, and Stew.

Picture of Add Oil, and Stew.

It doesn't really matter what polyethylene you use, you can melt HDPE plastic bottles in too, if you want.

That is, Resin Identification Code #2 and #4 are both good.

Polyethylene Terephthalate, that is PETE/PET or #1, may also work.

EDIT: Thanks to reader concern, I will state what may not be obvious from the pictures: there are no fumes. There's no smoke, no fans, no inhalation hazard. If there's smoke or fumes, you're doing something wrong and you're burning the plastic. That's why you use oil for temperature regulation.

The plastic bags do this alive-shrinky thing that looks really neat, so I took a video!

Step 3: Mash It

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When it's tacky like chewing gum, start mashing it around to get the different bag-lumps to stick to each other. A hand blender would be exceptionally helpful in this situation, but I chose to merely wreck one of my mom's forks instead.

Step 4: Get Moldy

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Now, while it's still pliable, put it into the form you want!

Since I'm just experimenting, I grabbed a salsa container that looked about the right shape for a wheel mold, and a wine bottle to make the hole in the middle.

I don't know any special techniques for molding and casting, but matt, rachel, bilal, paul, freemanmfg and smooth-on do!

If you were a molding ninja, you could make a plastic positive of your own face!

Step 5: Freeze

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Let it cool like cookies, or if you're impatient, make it cool faster in the freezer.

Step 6: Enjoy!

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There's the finished thing. It's got a lot of visual texture/color swirls, but it's actually a pretty regular surface. The circle turned out very well, and you can carve on this, machine it, turn it, and drill it, if you want something more precise.

This shows the finished product, the wheel, as well as another disc I made, and a video of just how surprisingly bouncy homemade plastic is.

Improvements to make:

I'd love to try using wax, instead of oil, so that the final surface is less greasy.
Shredding the bags beforehand would probably give a more homogeneous texture.

Also exciting! If you machined down a brick like this into large-ish chunks, you could feed them to your homemade injection molder! DIY action figures, hooray!


jacksonxbaj. made it! (author)2016-09-03

I have no Plastic Smithing experience but need some help/guidance. I'm an ice hockey player that has a permanent wrist injury/condition that makes it extremely difficult for me to hold my hockey stick correctly without pain. I'd like to construct a special custom made ergonomic insert/stick end that will allow me to play without pain. I'm not sure how to go about this (don't know if HDPE would be strong enough?). I found a photo (picture attached) of a hockey end-plug/stick-end that is no longer made or in circulation(off the market for like 10 years)....was thinking I could make something out of plastic that's strong like this (and has a few minor design alterations to suit my needs) - I might be able to start playing some serious hockey once again. Any advice/instructions/suggestions would be highly appreciated. Thank you :)

IDTrojan (author)jacksonxbaj.2017-12-10

If you can make a mold to approx shape you need (I use 2×4 wood and clamps), then do the final shape, sand, cut to the exact size ... Then yes you could make this it would be PLENTY strong enough. Trick is to use an oven, not oil and boiler; use only one kind of plastic; and apply as much pressure as possible during cool down. I built a little press with a 4 ton car jack. That made plastic parts as strong as steel!

Bobblob (author)jacksonxbaj.2016-10-30

Try InstaMorph thermoplastic pellets. It acts like clay when heated in hot water, but when it cools, it's a strong plastic. It can be shaped by hand when warm or filed, sawed and drilled when cool. More HERE Perhaps plastic bags can be used this way as well but maybe too hot to handle when heated enough to be soft?

bernardm47 (author)Bobblob2017-10-24

How much?thinking like a bkgnd.form for fish tanks ?toxicity?jat

dvorhis (author)jacksonxbaj.2017-08-29

Jacksonxbaj, It looks like your preferred modified handle has a slight bend in the end? If that's the extent of it, maybe making it out of a dense, strong wood (ash, maple, hickory, etc.) might be your easiest way to create a usable part. If your part is more complex, I could help you design a 3D model (gratis) that you could then have printed. I do this all the time for inventors who are designing something and need a prototype. The 3D printing technologies are rapidly coming down in price (HP Multijet) and going up in quality. Let me know if you'd like some help with this (

Melting plastic bags and bottles for reuse is a great idea - I have my eye out for a simple extruder so I can actually make fence posts for our farm. I won't be melting in an open kettle with oil, though - that is risky (fire) - but also weakens the polymer matrix.

ClaudiaN10 (author)jacksonxbaj.2017-03-22

Did you every get anybody to help? I have a suggestion for you. If you have a makers space in your area you could visit them and see if someone can help. We maker people love to help people. I hope you have good luck and be happy!

KarenP139 (author)jacksonxbaj.2016-09-10

If I wanted to make something like that I'd just 3d print it. More expensive, but a lot less hassle.

HDPE is pretty strong. That said, if you wanted to reinforce it you could try melting loose glass fibers into it.

KarlyleG (author)KarenP1392016-10-22

do you know where to get use of a 3D printer?

MichelleL64 (author)KarlyleG2017-01-24

Some libraries have 3D printers. Call and find out if your local library has one and if there's a charge. Our daughter's university has one but I don't know who is permitted to use it.

WilliamL219 (author)KarlyleG2017-01-11

Monoprice will sell you a small 3D printer for $200: If you don't trust Monoprice (?) you can build one for a similar amount.

tamidodel (author)KarlyleG2016-12-06

Go to they will make anything. You can design it or buy something that someone else had already made.

BoL11 (author)jacksonxbaj.2016-12-07

I have wrist problems as well. I use these on my sticks. works wonders.

RichardP213 (author)jacksonxbaj.2016-09-27

You might want to mold a folding stock that attached to the stick for a brace for your wrist a twisted cane shape would suffice. I don't recommend burning all this polyethylene real harmful to you and the ozone. Just save poly bags and take back to store

hblackorby (author)RichardP2132016-10-04

As the guy says in the article, you shouldn't be burning it. There should be no fumes. Your goal is to use low heat to melt it without creating any fumes.

IDTrojan (author)2017-12-10

Use a toaster oven ($10 at my local thrift store) heat HDPE, PP, PE or LDPE to 375-400F for an hour, take it out knead it like taffy, repeat 2-3 more times, then let it cool under pressure (I use a wood mold and c-clamps). You end with a hard, solid plastic with no voids that you can drill, cut, sand, polish into just about anything! I make tool handles, washers, repair parts, coasters, cutting boards, etc. The finished product is better and stronger than store bought!

SherylinRM (author)2016-06-18

Ok so how will I know exactly what type of plastic the bags are made of? Is there a symbol to look for or what?

Thanks :)

Sherbert- (author)SherylinRM2017-10-08

Plastic goods are supposed to have the resin code on them. Its difficult for Bags ( shopping bags ) The bags are 99 % of the time LDPE

JacobS160 (author)SherylinRM2016-06-30

Most plastic bags are polyethylene, high-density in the case of lightweight grocery bags, and low-density in the case of heavier department store bags (yes, you read that right...).

For other plastics, you probably already recognize the resin identification code, the little number inside the recycling symbol. Wikipedia gives the list:

SherylinRM (author)JacobS1602016-07-01

Thank you :)

PoconoMike (author)2016-06-13

Could I get opinions on whether or not my idea will work?
-Use an induction cooker to heat a pan filled with HDPE material and a little oil to about 250 degrees. Heat and stir until evenly melted. (I think the induction cooker has the means to maintain a steady temperature.)
-Make a wooden mold that uses a 2x4 for a bottom and has wooden sides and ends. Line the mold with parchment paper.
-Pour (or drop) the melted HDPE into the mold. Lay a piece of parchment paper on top.
-Place another 2x4 on top that's the exact same size as opening on the top of the mold. Clamp the top down and allow to cool.

This should create a solid block of 2x4 HDPE. The length will be limited by how much HDPE I can melt at one time. I'm hoping I can create 2x4 lumber and build a small bench.

Sherbert- (author)PoconoMike2017-10-08

Have you tried this ? It should work ! Will be good to hear your result

Bowlgouge (author)PoconoMike2016-07-24

There are mold release waxes that you can apply to your forms.

JacobS160 (author)PoconoMike2016-06-30

Strictly speaking, wouldn't the oil be unnecessary (except as a thermometer)? I don't expect it'd ruin anything, though. Wood and parchment paper catch fire at 300F and 400F respectively, so should be no surprises there.

As for the mold, your plan has you creating essentially a square tube. It could be challenging to make the fit perfectly tight with zero bowing along a void for a full 8' 2x4, but I also don't think a perfect fit would be necessary. I think the bigger potential source of problems would be in lining this tube with parchment paper. Just getting it in would be one challenge; you could possibly wrap the parchment paper around a clean 2x4, insert the lumber and then remove it, leaving only the paper lining. But even then, you would need to arrange the parchment paper in such a way that it can't pop out and stick out into the void; you don't want the paper to get caught on the plastic, folding up
and crumpling and pressing marks into your final product.

I think a safer way to ensure a smooth final product would be to make a mold that opens up along the length of the 2x4, instead of just at the ends. This would make it easier to work with the parchment paper liner: you'd just clamp a flat lid over it all once the mold is full. I admit, though, that such a system wouldn't have as much flexibility to account for varying amounts of plastic. It might be possible to make the mold extendible by building it a bit like a pinewood derby car track: long and shallow, with one of its ends (the "car") movable so that the void can be lengthened or shortened as needed.

KarenP139 (author)2016-09-10

I tried melting a block of polyethylene in an oven today. There was a lot of smoke and the outside was starting to brown The polyethylene had softened (and gone transparent) but was not at all melted. There's a chance that the smoke was at least in part from paraffin left over on the tray from the last thing I melted, but that wouldn't explain the browning. Is it normal for the polyethylene to do this? I'm surprised I didn't get any melt at all.... maybe it needed more time, but with the smoke and browning, I didn't want to risk a fire.

Is the oil how you prevented smoking/browning, aka keeping it away from oxygen? Does it just melt at the bottom of the oil? How do you separate the polyethylene from the oil? Can you just pour it off? My purpose of melting it is to coat some aluminum tube segments.

I could always try melting it in a microwave (in a glass jar), but I only have one microwave and don't want to ruin it... I tried setting things up to melt it with an acetylene torch outside but couldn't find a lighter that worked, and didn't have the nenn to go to a store and pick up a new one :Þ

Sherbert- (author)KarenP1392017-10-08

don't try the microwave. It wont work. ! Microwave needs water ! it cant heat dry stuff

KarenP139 (author)KarenP1392016-09-10

Just an update... I tried it in a pan on the stove, with a layer of oil over it. First I tried motor oil, thinking that it'd be a lower risk of burning, but it very quickly started giving off a bad smell, so I wiped up what I could and replaced it with cooking oil. I've hit a point where it's not melted, but I'm not comfortable turning up the temperature any more because of the amount of plastic (or residual motor oil?) smelling smoke coming off of it. So again no luck :(

KarenP139 (author)KarenP1392016-09-10

Okay, it gets weirder. Now that it's cooled I could check each individual component. The smell seems to be coming from the plastic, not the oil. The oil just smells like used cooking oil. However, the oil does not *look* like normal used cooking oil, it looks... don't know how to describe it, "partly polymerized"? Like, still fluid, but slightly gelled, or containing some slightly gelled material? Yet it's far too cold for polyethylene.

Not sure what's going on here....

KarenP139 (author)KarenP1392016-09-10

(might just be that the oil was thick to begin with, I don't know)

Mz Pippa P (author)2017-08-25

Could an outdoor turkey cooker work for melt heavy mill black plastic bags,industrial kind unused. Then put melted bags between to OLD 2X4s then use those for molds. Old wood would have deeper grain & splits The weight to press the molds would have be even or you would make worpped lumber. I would like to make all the materials to build a " tiny " house or tiny castle. It would be a great roof , pathways, doors ...But would it pass code?

Chimonger (author)2017-05-24

Pretty cool! Someone some years ago, learned that by mixing different plastics together and form bricks, the resulting bricks were stronger than regular bricks...something about cross-linking polymers.

Your donut blocks could be interesting as stacked on rods, maybe chicken wire on both sides then plastering inside and outside of the "wall". Or make a mold that could do a double-donut [an "8"], do the blocks could be interlocked on rebars.

linda.hartman.3950 (author)2016-06-02

How would you die this material for making lumber. I guess you could make a lumber form and pour/place/pack the material in the form. People have said the material should be pressurized while drying. Guess you could use bricks or something else for this purpose? At any rate, here is a link to making plastic lumber.

to color this material any powder based pigment will work one excellent source i have used was powdered charcoal what i did was i used milk jug plastic than melted the plastic down kneaded in the charcoal into the melted plastic using silicon gloves than clamped it down into a mold the result was a completely uniform black colored piece of plastic that was also uv resistant due to the charcoal

NeciaL (author)funny10482017-04-29

I like the idea of being able to colour, could you also colour the plastic bags with this method. How much time to you have to mould using the gloves before it sets, I might want to try doing something a little intricate so time is of the essence.

SigynS made it! (author)2017-03-18

Crockpot works- though putting a mold inside might be smart Hehe~

SigynS (author)2017-03-17

I read down pretty far, but did not see any comments on using a slow-cooker....they reach almost exactly that(for the non-digital ones)


StevenT105 (author)2017-02-07

So... I done tried this and it actually works a lot better if you don't shred the bags, because the more shredded it is the harder it is to mash and the worse it looks. I stuffed all the bags inside one bag and it came out with much fewer wrinkles, it was less oily and was easier to work with.

I also tried it with wax. That was weird. The wax seemed to dissolve the bags rather than just melt them, so I had a weird plastic/wax goop that hardened rather quickly. I found it to have the same texture as wax but be much stronger than wax. However compared to the oil plastic it was much more brittle and won't hold up well. But it did have almost no wrinkles in it all.

yrralguthrie (author)2016-11-17

I find it easier to add 40 to the temperature either Fahrenheit or Celsius and then either multiply by 5/9 if going from larger number (Fahrenheit) to smaller number (Celcius). Then subtract the 40.

If going from Celsius to Fahrenheit do the same thing except multiply by 9/5.

Celsius to Fahrenheit is particularly easy since I just round off the Celsius temperature to a multiple of 5.

Add 40, multiply, subtract 40

delsur (author)yrralguthrie2017-02-07

I can no longer do any math in my head. I find it easiest to key in

248 F =

on the line used for the URL in my Chrome browser.

Chrome will do other conversions for you, too.

SyamimF (author)2017-02-04

Is it possible to make hdpe pipe then by this diy method ?

auto13142828 (author)2017-01-19

California just outlawed plastic bags.

LeVolatile (author)2017-01-18

Would it be not a lot simpler if everybody use Celcius and all metric measure? Think about it! I learned everything in Imperial while I was a child and I had to convert myself to metric in the 70's when Canada decided to go metric. Its not that hard! I think the best way to do it is by "thinking in metric", not trying to convert everitime. For example: Think about 22 C is a confort zone room temperature. -10 C is moderatly cold winter day, etc

cesarakg (author)2016-06-02

Just a note, 248°F (fahrenheit) equals to 120°C (celsius).

Google told me that (

Pa1963 (author)cesarakg2016-06-02

My old conversion math say Fahrenheit to Celsius is 5/9 minus 32. So 105 deg. Celsius?

yrralguthrie (author)Pa19632016-06-02

When going from F to C you have to subtract the 32 first then multiply by 5/9.

120 is correct

x 9/5 + 32 = °F

(°F - 32)
x 5/9 = °C

ok then

LonnieA2 (author)yrralguthrie2016-11-17

I LOVE that you know that. The other night at Willy Wonka rehearsal, one line Wonka says is that Augustus "...will be heated to 88 degrees Fahrenheit...or it is Celsius? I always get the two confused, often with disastrous results." The director asked if anybody knew how hot 88 degrees Celsius was in Fahrenheit. I wanted to raise my hand (at age 47) and say, I cannot do it in my head, but it is equal to 88 times 9, divided by 5, plus 32. :-) Of all the things I learned from Mr. Stone in 4th grade science class, the F to C and C to F conversion formulae have served me the best all these years! CHEERS!

Pa1963 (author)Pa19632016-11-12

Thanks for the correction.

catsoori23 (author)2016-07-08

Is there any risk in making this?

JG46 (author)catsoori232017-01-07

I worked at a polyethylene plant for 9 years. PE is a great material, self- lubricating, light, translucent, and very tough when properly moulded. It's also so inexpensive that the oil used above will cost more than the plastic film is worth. Things to avoid include flammable ethylene fumes, fire, spills, splashes and burns.

I especially like Bobblob's comment upthread re the InstaMorph thermoplastic pellets as an alternative project. The pellets give much better control than old bags if used per the directions.

aprizt74 (author)2016-12-11

Guys, sory to bother i have a question for i dont have any experience in this. And planning to mold HDPE (from old oil containers). If using oil/wax when melting the plastic will it just separated like oil-water mix or will i have to separate them? And how? I think it will be a problem if any oil get poured to the mold with the plastic.

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