# Closest synthetic that is as stretchy as Latex

ktoz
TL;DR Summary
Need a tough, durable and stretchy material for a project I’m working on.
Hi

I’m working on a prototype idea and think I could greatly simplify one part if I used some sort of tough stretchy rubber. Something that offers good spring-like resistance and a fast rebound.

I googled many different combinations of “latex like synthetic” or “stretchy synthetic rubbers” etc, but the best that came up with were general articles stating there are many different kinds of rubbers.

I need something that will stand up to years of stretching without degrading, like latex.

Something as stretchy as the rubber tubing used for slingshots, but that won’t degrade or get gummy, like old rubber bands.

The loads will be pretty light but it needs to weather well and spring back forcefully.

Does any such material exist?

2021 Award
Is it stored for long periods under tension, neutral, or compression ?
What is the geometry of the material ?
What percentage of stretch is required ?
What is a light load 1kg, 100 kg ?

ktoz
It’ll need to be under tension, but not stretched to its max.

Flat would be best (to make the part smaller), but I could live with round.

Percentage stretch is just a guess. Say something like slingshot tubing pulled back about half way.

Load is also just a guess. Maybe the force needed to stretch a wide rubber band. 10 to 15 pounds?

For the prototype, I could probably get away with a rubber band, but before committing to the idea, it would be helpful to know that after prototyping is done and tested, there is a material that could be used in the real part.

Sorry for the non technical terminology and descriptions, but I know nothing about the properties of various rubbers.

Homework Helper
As a kid I remember making mediocre slingshots out of butyl rubber bicycle inner tubes.
You should talk to a rep from a supplier of silicone rubber...usually they will be happy to talk. I don't know what the limits there are

sysprog
Mentor
Go to the McMaster-Carr website at https://www.mcmaster.com/, then enter elastomer sample pack in the search window. The price of one or several sample packs is cheap compared to the value of having something to hold and pull on. The photo shows a typical pack that I bought several years ago when I had a similar question:

There are several different durometer (search the term) scales. The 30A and 40A durometer have similar stretchiness as rubber bands.

Then search urethane and elastomer on that web site. Some urethanes can stretch to as much as 5 times their original length. They also have castable urethanes. Those work, but it's difficult to get the air bubbles out. Something I learned the hard way.

berkeman, sysprog, ktoz and 1 other person
ktoz
Go to the McMaster-Carr website at https://www.mcmaster.com/, then enter elastomer sample pack in the search window. The price of one or several sample packs is cheap compared to the value of having something to hold and pull on. The photo shows a typical pack that I bought several years ago when I had a similar question:
View attachment 287546
There are several different durometer (search the term) scales. The 30A and 40A durometer have similar stretchiness as rubber bands.

Then search urethane and elastomer on that web site. Some urethanes can stretch to as much as 5 times their original length. They also have castable urethanes. Those work, but it's difficult to get the air bubbles out. Something I learned the hard way.

Thanks for the info! Seems like a good way to get an intuitive feel for the various types.

berkeman and jrmichler
Mentor
They also have castable urethanes. Those work, but it's difficult to get the air bubbles out. Something I learned the hard way.
Depending on the shape that you are casting, you may be able to use vacuum casting to make the bubbles a lot smaller (releasing the vacuum after injection shrinks the bubbles). We used vacuum encapsulation for an epoxy-encapsulated network transceiver module that I worked on. We needed to shrink the bubbles to a size smaller than the smallest conductor feature size in the product, to prevent reliability problems due to copper migration inside the microclimates of the bubbles.

We used Liquid Control Corporation in Canton Ohio (now a division of Graco) to help build the custom vacuum encapsulation machines (we've had them build several of them over the years for us, that transceiver sold in the tens of millions, and is still an active part):

https://www.graco.com/us/en/in-plan...silicone-rubber-lsr/lsr-metering-systems.html

ktoz
Depending on the shape that you are casting, you may be able to use vacuum casting to make the bubbles a lot smaller (releasing the vacuum after injection shrinks the bubbles). We used vacuum encapsulation for an epoxy-encapsulated network transceiver module that I worked on. We needed to shrink the bubbles to a size smaller than the smallest conductor feature size in the product, to prevent reliability problems due to copper migration inside the microclimates of the bubbles.

We used Liquid Control Corporation in Canton Ohio (now a division of Graco) to help build the custom vacuum encapsulation machines (we've had them build several of them over the years for us, that transceiver sold in the tens of millions, and is still an active part):

https://www.graco.com/us/en/in-plan...silicone-rubber-lsr/lsr-metering-systems.html
I’m kind of a vicarious bowl turning fanatic. (Don’t currently have space for wood lathe) Pretty much all of the guys I watch who use resin in their bowl turning, use either vacuum chambers and or pressure pots to remove bubbles.

The thing I’m designing is very much a niche product. If it “took the world by storm” in its target market, I doubt that all units ever sold would come anywhere near your transformer. At most, I see maybe a few hundred units will ever be sold. The target price I’m shooting for is in the range of $5000 to$10000 a piece.

Not going to turn me into Bill Gates.

berkeman
Staff Emeritus
People make expoxy resin table tops and they do pretty good on eliminating the bubbles using the flame from a torch.

What are the dimensions of your product?

What is your tolerance for bubbles? How many? What size?

ktoz
People make expoxy resin table tops and they do pretty good on eliminating the bubbles using the flame from a torch.

What are the dimensions of your product?

What is your tolerance for bubbles? How many? What size?
Basically the thing I want to make is a glorified rubber band. Maybe 1.75 to 2.5 inches in diameter, wall thickness of 1/8 to 5/32 inches with a width of between 1/4 and 1/2 inches.
Each device gets one and I see a runaway success for sales of the devices as no more than 100. (they will be sold in sets of 20) So maybe 2000 bands, tops.

Staff Emeritus
If you can make underwear where the elastic waistband doesn't get old, I'll buy some.

Have you experimented with passing a torch flame over the curing liquid in the mold?

When you say weather well, what about UV? Will it be exposed to sunlight?

Edit: Thomas Edison famously said, "Genius is one per cent inspiration, ninety-nine per cent perspiration" Having a good idea, then asking strangers on the Internet how to make it, does not count for much perspiration.

Last edited:
ktoz
If you can make underwear where the elastic waistband doesn't get old, I'll buy some.

Have you experimented with passing a torch flame over the curing liquid in the mold?

When you say weather well, what about UV? Will it be exposed to sunlight?
Haven’t finalized the design yet, so It’s a little early for molds.

It’ll be fully encased, so no UV problems. Maybe grease, for the metal parts, if slippery plastics, like Acetal or UHMW require it. I’m basically looking for a material that won’t turn gummy, or dry out and weaken if left in a drawer. It would make sense to buy all of the bands, up front, and keep them on hand for build on demand unit sets. Usage life should be 5 to 10 years.

P.S I hear you on the underwear bands.

Mentor
Basically the thing I want to make is a glorified rubber band. Maybe 1.75 to 2.5 inches in diameter, wall thickness of 1/8 to 5/32 inches with a width of between 1/4 and 1/2 inches.
Take a look at square section O-rings. Here's a supplier (not the only one, but they have a good website): https://www.mcmaster.com/o-rings/square-profile-oil-resistant-buna-n-o-rings/.

You could get the width you want by gluing two or more together. O-rings last a long time, and are available in different materials with different stretchiness.

berkeman
ktoz
If you can make underwear where the elastic waistband doesn't get old, I'll buy some.

Have you experimented with passing a torch flame over the curing liquid in the mold?

When you say weather well, what about UV? Will it be exposed to sunlight?

Edit: Thomas Edison famously said, "Genius is one per cent inspiration, ninety-nine per cent perspiration" Having a good idea, then asking strangers on the Internet how to make it, does not count for much perspiration.

Heh. That edit makes some pretty big assumptions. I assure you, I’m putting in plenty of effort.

Besides, Edison wasn’t a lone genius toiling in his garage. The idea for a light bulb had been around for years. He succeeded primarily because he knew he couldn’t learn everything and hired a whole team (and even a physicist) to work the problem.

ktoz
Take a look at square section O-rings. Here's a supplier (not the only one, but they have a good website): https://www.mcmaster.com/o-rings/square-profile-oil-resistant-buna-n-o-rings/.

You could get the width you want by gluing two or more together. O-rings last a long time, and are available in different materials with different stretchiness.

Thanks. I’ll look into it. Ordered the elastomer sample pack from them Sunday.

berkeman and jrmichler
Mentor
Take a look at square section O-rings.
Oh dear. My 4-pass parsing algorithm failed, so I had pass over the post. I came back a minute later to try again, and managed to rotate my mental axis system enough to understand it. Clicking on the link verifyed what I finally figured out. LOL

ktoz
After several days of searching, I found the perfect solution for my “stretchy non-latex” material, designer rubber bands from Grafiti Band Joe’s. They even come in approximately the right size, are pretty cheap and come in lots of cool colors. (Although no one will ever see them)

https://grifiti.com/products/grifiti-band-joes-1-25-inch-silicone-rubber-bands

Thanks all who took the time to answer

berkeman and Tom.G
Kenwstr
I found a short off cut or marine shock chord among bits from my youth 1970s.
It is still in excellent working condition. Unlike the stuff I can buy these days which only lasts 1 or 2 seasons. This still has very high strength & I'd have no hesitation using it if it was a useful length. It has an outer monofilament nylon braid, unlike any that I have seen in recent years. I don't know what the material is but maybe ask around marine suppliers. Whatever it is, has lasted far better than any other elastic material in my experience. It still appears and works like new. I still have a kayak spray skirt that I made in those days using this elastic & it's still serviceable after decades of use in salt and fresh water. I have never replaced this elastic. Sorry I just don't know what it is but it seems to indicate that something suitable for your application exists.

berkeman
Mentor
Unlike the stuff I can buy these days which only lasts 1 or 2 seasons. This still has very high strength & I'd have no hesitation using it if it was a useful length. It has an outer monofilament nylon braid, unlike any that I have seen in recent years. I don't know what the material is but maybe ask around marine suppliers. Whatever it is, has lasted far better than any other elastic material in my experience.
Interesting. Paging @anorlunda @sophiecentaur

Staff Emeritus
Gold Member
Interesting. Paging @anorlunda @sophiecentaur
I've only ever bought regular eBay style Bungie Cords and tended to avoid the equivalent stuff you get in ships' chandlers. I always assumed they were merely the same thing with a higher price tag.