by David Claus, Ph.D.

When it comes to casting body parts, you don't ever want to use one of those industrial silicones found at places like Home Depot.  Why not?  Because they're NOT SAFE for your body.  Aside from that, they won’t be able to capture any fine details, they're relatively unstable, and they'll shrink and/or deform during cure.

They're not body safe

The tubes of silicone you see in hardware stores are indeed silicone, but they're what's called condensation-cure or tin-cure silicones, not addition cure silicones like those used in body casting.  Though based on the same core structure: silicone+hydrogen+oxygen+carbon, the way each cures or hardens makes them essentially two entirely different materials. 

Condensation-cure silicones are formulated for industrial uses only, meaning they must be made cheaply and must work easily... no mixing required.  All you do is expose a condensation cure silicone to air and it will begin to cure.  Simple and cheap, right?  And great for home uses like sealing leaks around your bathtub. The problem is that this type of reaction releases toxic gasses when exposed to air or water.  Try this: open a tube of a hardware store silicone and take a whiff. You’ll notice a strong, sour-like odor. This is the sign of a condensation-cure silicone. The chemical reaction that occurs when you expose this kind of silicone to water (or air) forces the release of toxic byproducts in the form of acids and/or potentially toxic alcohols. Even after this type of silicone has cured, it will continue to emit a potentially toxic odor for several days (actually for years, though it won’t be detectable by your nose). There are newer ‘odor-free’ versions, but they’re still condensation-cure tin silicones and will still release toxins - the odor has just been masked.  

The silicone in your Clone-A-Willy Kit, on the other hand, is an addition-cure platinum silicone, which is completely safe in all its forms. A finished platinum-cure silicone is made up of the same basic structural elements as a tin or condensation-cure silicone (silicone+hydrogen+oxygen+carbon), but the reaction stops when all of the platinum has been utilized (bonded) in the reaction. This ensures that the molecular structure is completely stable. Your finished piece will not break down, become brittle, or deform over time.  Additionally, no toxic gasses are released while it cures. There is no smell and nothing harmful within the material whatsoever. Clone-A-Willy Kits utilize what’s considered a medical-grade silicone, meaning once cured it’s completely stable and will never outgas or react with the body in any way.  Inert silicones of this type are formulated specifically for use in medical applications, and are completely safe when exposed to the outside or inside of the human body.

They won’t capture fine detail

Aside from the potential dangers above, condensation cure silicones are very viscous (thick). This high viscosity leads to a major problem: they're too thick to properly and completely fill a mold cavity. These silicones are specially formulated for industrial uses, and they work well when used in thin layers as sealants, adhesives, insulation, etc. They do not work well when curing inside a mold, however. Even when poured into a beautifully detailed mold, they won't be able to fill all the small nooks and crannies inside. They're just too thick. In addition, it will be virtually impossible to expel all of the multiple, large air bubbles that form once the silicone is poured into your mold. If you were to use these silicones for casting, the result will be a copy that looks like little more than a blob of bubbly goo. They are simply not designed for body casting.  

What makes copying a body part interesting and fun is seeing a true, detailed representation of the original.  Only a less viscous, platinum cure BODY CASTING silicone, like the one in your Clone-A-Willy Kit, will give the detailed results people want. When it comes to penis casting, you'll definitely want a true-to-size and shape copy, not something shrunken or deformed!  And you'll want more than an ill-defined blob - you'll want a silicone that will capture every minute little detail that makes you unique.

They tend to shrink and/or deform

Another problem with using a tube of construction silicone to cast a body part is deformation. The reason these silicones are referred to as condensation-cure (or tin cure) is that they cure when exposed to water or O2. Even after initial curing, this reaction is not finished. It will continue to take place very slowly over days and years, causing shrinkage, deformation, and brittleness. A tin cure silicone will continue to react to moisture, sunlight, and other environmental exposures. Aside from not making an accurate copy in the first place, it will continue to break down further and even lose more of it's properties over time.  A platinum-cure body casting silicone, like the the one in your Clone-A-Willy kit, sets up fully and completely within hours, and it will NEVER shrink or break down!  

So what’s the takeaway? When it comes to casting a body part, ESPECIALLY a penis that’s intended for use inside the body, use only a stable, body-safe, medical-grade platinum-cure silicone!