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Silicone lube & silicone toys: chemistry lessons for the sex-toy-curious

As a sex educator and sex toy retailer, I've been trained to warn people that silicone toys aren't compatible with silicone-based lube, and that using these together will ruin your precious (and probably quite expensive!) toys.

But over the years, some folks - myself and many of my colleagues and customers included - have started to question this standard and oft repeated edict after seeing that it doesn't necessarily match up with many people’s actual experiences using silicone lube with silicone toys.

In response to these experiences, the default correction that I’ve often heard and seen repeated throughout my online research is that quality silicone lubes can often be used with quality silicone toys (but not always… it depends on the chemistry… it’s complicated). 

This explanation never quite made sense to me, because the more I thought about it, the more questions I had. Like, why only quality silicone toys and lubes? Is the issue with the additives or the actual silicone? And why would some quality toys be the exception to the rule but not other - equally as good quality - toys? Aren’t chemical reactions more consistent than this explanation suggests?

I needed to know more.

Silicone lube + silicone toys: best practices 

But before we get to the bottom of this scientific conundrum, here are some practical things you can do to keep your toys safe if you’re using silicone-based lube with your silicone toys:

Do a patch test

This is best done somewhere inconspicuous on your toy, e.g. on the base of a dildo. Dab a little silicone lube on the surface, rub it in, and leave it overnight. If the two aren’t compatible, your toy will get gummy or tacky to the touch.

Use a condom

Cover your silicone toy with a condom (preferably unlubricated!) Lubricated condoms have a bit of silicone-based lube on both the condom’s interior and exterior - usually not enough to harm a silicone toy, but there is a small risk.

Avoid any silicone lube with dual-density toys

Never use silicone lube - lubricated condoms included - directly on dual-density silicone toys, and beware of using it on any of your softer toys.

Wash your toy

If you’ve paired silicone lube with a silicone toy (without a condom), wash the toy immediately after using it (a good practice, regardless).

A quick heads-up

Things are gonna get pretty technical, so if you're not especially interested in the science of silicone, you might want to slide on outta here right about now!

Going to the source (of satisfying answers!)

In my search for answers to the question of why some silicone toys are fine to use with some silicone-based lubes but not others, I contacted the friendly and knowledgeable folks over at Fuze Toys.

Co-founders Mark and Susan have been in the silicone toy manufacturing business for over 20 years, and produce only the best quality toys while maintaining a strong focus on environmental stewardship, inclusive design and ethical production.

Over our many years of working together during my time at Other Nature, Mark and Susan have been incredibly generous with their time and industry knowledge, always willing to share their insights with me, no matter how technical or basic my questions. And when I reached out this time, it was no different!

The Lube Lady and the Toy Maker talk chemistry

Mark isn’t a chemist and doesn’t claim to be one. In fact, he specifically asked me to make clear to my readers that he’s not an expert in the field of professional silicone formulation. Still, he clearly knows lots of stuff about silicone from his many years of making silicone toys and working closely with actual experts and silicone formulators.

Before getting to the topic at hand, Mark and I discuss some silicone toy chemistry that serves as an important building-block for my questions about toys and lube.

Me: Given that they’re all made of silicone, why are silicone toys so different from each other, with some being quite firm and others softer and more flexible?

Mark: Silicone is made from long chain molecules using a strong silicone-silicone bond and silicone-oxygen bond. Hydrogen is also present, as are some other elements in lower amounts. Different fillers can be added to the formulation to achieve specific results.

The long chain gives silicone its strength, so the longer the chain, the stronger the material. Also, the more bonds that form between each chain, the more rigid the final material.

However, the flexibility [of sex toys] is a result of open bonds and fewer connections between the molecule chains made during the curing process, allowing them to move against each other. So the more open bonds, the more movement between the chains and a softer, more flexible material. However, this results in a weaker silicone which is more prone to damage.

Me: By “weaker”, do you mean lower quality or simply more delicate? 

Mark: Calling the silicone weaker has nothing to do with the quality of the silicone. Soft silicone can be of equally high quality to firmer silicone, it simply has different physical properties. Softer silicone has to be handled more carefully to prevent damage or tearing.

Me: How do you achieve the desired amount of toy-flexibility in the production process?

Mark: There are two ways to reduce the number of bonds between the long silicone chains. The first is to create a pure silicone formulation of a specific durometer working from the basic atoms up. This is a highly specialized process that requires extensive research and development. Creating a custom formulation is therefore extremely expensive. This is the route that Fuze always takes.

The second way is quick, cheap and easy. You simply take a standard silicone, say 20 durometer ShoreA and add a liquid silicone, di-methyl siloxane fluid (DMF, also known as poly di-methyl siloxane or dimethicone). DMF forms a partial liquid barrier between the long chain silicone molecules during curing, so there are fewer cross bonds and a softer resultant silicone. The higher the percentage of DMF the softer the material. However, since DMF remains in liquid form it is not fully trapped between the solid silicone chains and will leach out over time. This is why very soft silicone tends to be oily feeling, and over time will shrink and warp. This is most noticeable for double durometer toys, the firm inner contains less DMF so will not shrink to the same degree and you will see a step where the two silicones meet.

Me: So with the method that Fuze uses, you manage to make toys soft and flexible without adding Dimethicone. What are the main advantages to this process, given that adding DMF is much faster, cheaper and easier?

Mark: Just to be absolutely clear, there is nothing wrong with DMF. It is regarded as being completely body safe and can be found in everything from silicone based lube to shampoo. At Fuze we have chosen not to take advantage of DMF because it would affect our silicone toys in ways that we would not find acceptable.

As DMF leaches out over several months, a toy that had initially been very soft will actually start to feel noticeably firmer. Silicone that has been softened by the addition of DMF will be more prone to damage and tearing than silicone of a similar softness where DMF has not been used. If a toy made with DMF is stored touching a toy that was made without DMF, the DMF can leach out and damage the other toy. Over time, silicone toys that have DMF leaching out of them can shrink, change shape and develop new warps and twists.

Me: And what about Platinum curing? This term is often used as a signpost for high quality toys. Where does it fit into these processes? 

Mark: Talking of platinum cured silicone is a way to distinguish between two different silicones, each developed for a different purpose.

Silicone as a raw material is a thick liquid, with a consistency a bit like molasses. The liquid silicone is turned into a solid by mixing in a catalyst. The two commonly used catalysts are tin based and platinum based.

Silicones using a tin based catalyst are also known as condensation cured silicones. They are cheap, have excellent physical properties and are great for use by artists and industry. Unfortunately, tin silicones release formaldehyde during curing and are not as body safe as platinum silicones.

Silicones using platinum based catalysts are also known as addition cured silicones. They are more expensive, and also have excellent physical properties. Importantly, platinum silicones do not release formaldehyde, are completely body safe and are used for medical devices . This is the standard of silicone that should be featured in all silicone toys.

Me: Now that we’ve established some important foundational knowledge, can you tell me what you make of the claims that quality silicone toys are often compatible with quality silicone lubes? Is this true? 

Mark: The statement that high quality silicone toys will not be affected by silicone lube has not been borne out by the controlled experiments we have done. 

One problem is that silicone toy manufacturers do not list the exact formulation, the second is that lube manufacturers do not list the exact formulation either.

As it was explained to me by an expert in the field, the "quality" of the silicone toy [or lube] is not the important bit. What is important is how similar the silicone in the lube is chemically to the silicone in the toy. The more similar they are, the more likely they are to combine, conversely the lower the chemical similarity the less likely they are to interact.

Equally, the higher the proportion of open bonds, the more likely there will be interaction between lube and toy. 

This is why some toys are safe with some silicone lubes, but not others; and some lubes will interact with some toys, but not others.

Me: You said before that having more open bonds creates a softer/more flexible toy. Does this mean that softer toys are generally less compatible with silicone-based lube? 

Mark: Yes, softer toys have more potential bonding sites with the silicone in lubes, so an interaction is more likely than between firmer silicones and lubes. 

Softer silicone with DMF added has bonding sites available on the long molecular chains of the solid silicone, and in the DMF polymer, so an interaction is even more likely. Also, the presence of DMF within the solid silicone allows increased diffusion of molecules from the lube into the toy, thus further increasing the chances of interaction.

[In sum] softer toys are more likely to interact with lubes. Toys containing DMF are more likely to interact with lubes than toys without DMF as di-methyl siloxane is extremely similar to the liquid silicone in lubes.

Me: If we knew the chemical formulation of different toys and lubes, would we be able to come up with more concrete rules around which toys to use with which lubes (e.g. “X company’s toys are compatible with Y company’s lube”)?

Mark: The only way to be certain that a specific lube will not damage a specific toy is to do a patch test on each toy with each lube. The results cannot be extrapolated even for toys from the same manufacturer. Our 30 durometer, 20 durometer and 10 durometer silicones all have very different chemical formulations

Even looking at chemical similarity is just a rule of thumb and has exceptions. For example addition cured silicones are completely different chemically to condensation cured silicones, but the two will stick together to form one solid mass.

Some of the larger manufacturers may source their silicone from several formulators, so different batches of the same toy from the same manufacturer may have different chemical properties, but the same physical properties. Even the pigment used for the silicone toy can have an effect, for example an aluminium based pigment will make interaction with a lube more likely than a mica based pigment. (Fuze does not use aluminium based pigments.)

This is why we have blanket advice of "Don't" when we are asked if silicone lube can be used with silicone toys, even though it may be no problem. It saves potential disappointment and a lot of hard work doing multiple tests.

Me: Mark, thank you SO MUCH for your time, patience, and willingness to go deep into the chemistry with me! I hope our conversation will satisfy all the other toy freaks and lube geeks out there :)


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