Natural Latex Foam Rubber is quite unlike any other material on the planet. It compresses and stretches, is light, springy and bouncy and reproduces intricate detail. Unlike slip cast latex ‘shells’, latex foam is a solid material. It is not difficult to make as rumor might suggest, requiring a level of skill similar to cooking, mold making or wood working. Given that you can read and follow instructions, there’s every reason you’ll have success within a few foam runs. Once you get the hang of it.
Puppeteer Bil Baird may have been the first to use latex puppets on American television with Poutapoof and latex foam for automotive ‘gear’ puppets at the 1964 New York Worlds Fair. At Baird’s in the 1970’s I had the opportunity to examine these gear puppets. They were made of tough latex foam with a coarse cell structure, quite crude by today’s standards. Bil told me the process then was so hush-hush he wasn’t allowed to watch and sent molds to the factory to be filled. Bil never went into latex foam in a big way, preferring to stick with the slip cast latex puppets he pioneered and knew so well.
Jim Henson was the first to use latex foam puppets on a large scale. First duplicating Miss Piggy, Statler and Waldorf for the international hit series The Muppet Show followed by Jim’s groundbreaking film The Dark Crystal. Designed by British fairy artist Brian Froud, Jim's vision for this fantasy world inhabited exclusively by puppet and anamatronic characters pushed the limits of many diverse technologies. The author and several assistants created hundreds of latex foam puppets and props for the film. If you have never seen it, make a point to get it out on video.
Suddenly modern puppetry grew up. Any thing that could be sculpted could now be duplicated in flexible latex foam and made into a puppet. From hard edged realism to soft and cuddly, if you can sculpt it and mold it you can probably make it into a latex foam puppet.
Puppet foam is quite different from industrial foam used for bedding and carpets and is best described as ‘Theatrical’ Latex Foam. It is velvety soft and pliant, it’s cell structure very small to pick up fine detail and uses high solids latex for strength and to keep shrinkage down. It's ideal for Puppets, Animatronics, Stop Motion Puppets, Makeup Appliances, Toys, Dolls, Props, Fantasy Costumes and Creature Suits. To this day latex foam remains the backbone of the special effect industry for flexible characters and illusions.
Latex Foam can be made with a relatively small initial investment. It can be cast into inexpensive gypsum (hard plaster) molds and small pieces may be baked in a household oven if need be. It is sometimes called ‘hot foam’ to differentiate it from ‘cold foam’ polyurethane foams. Latex Foam’s ability to pick up fine detail and its subtle movement have yet to be matched by any polyfoam the author is aware of. Latex Foam manufacture is a manual process. It is not difficult but does require attention to detail, keeping meticulous notes and understanding several concepts unique to its nature.
FOAM KITS: Kits come with all the components and instructions you need to make latex foam. A quart kit is the smallest available with material for about five 150 gram batch foam runs, enough for 5 small or 2 good sized puppet heads plus hands. A gallon kit is good for upwards of 2 dozen small or 10 good sized puppet heads and a few sets of hands. 5 gallon kits will do dozens of just about any size puppet parts you conjure up, or a few big pieces. Body suits might require an entire 5 gallon kit or more. NOTE: Each brand offers kits with all the materials you need. Some brands use different formulas or fewer components. Follow each manufacturer’s formula and instructions for best use of their materials.
1) Measure / Weigh Latex, Foaming and Curing Agent. Gelling Agent in separate cup.
2) Froth Latex Mixture in Food Mixing Machine on High Speed.
3) Refine / De-Ammoniate at Low Speed.
4) Add Gelling Agent and thoroughly Mix in - add color, if used.
5) Cast into Pre Released Molds.
6) Cure in Oven.
8) Wash and Dry.
LATEX FOAM MATERIALS (4 part system)
Latex Color (optional)
LATEX FOAM EQUIPMENT
Room Thermometer, Oven Thermometer
Scale or Measuring Cup and Spoons
Plastic or Paper Cups / Mixing Stick
Variable Speed Electric Food Mixing Machine with Bowl and Whisk(s)
Apron / Protective Clothing / Protective Gloves
Ventilation and / or Fume Mask approved for Ammonia
Protective Eye Wear if sensitive to ammonia fumes
Foam Log / Note Pad / Pen / Pencil
THE FOAM RUN: Apply release to mold, let dry, brush out excess. Measure Liquid Latex Foam Base, Curing Agent and Foaming Agent and mix together in cup. Measure Gelling Agent into a separate cup at this time for later use. Place Latex, Cure and Foaming Agent mixture in electric food mixer bowl and froth with whisk(s) at high speed until desired air / latex ratio (volume) is achieved. Once desired foam volume is reached turn mixer speed to low to refine air cells and drive off excess ammonia (de-ammoniation). When most of the ammonia has been whisked off and foam cells are uniformly small, delayed action Gelling Agent and any color are added and thoroughly mixed in. Be careful not to introduce new air bubbles. Scrape down sides of bowl with spatula if required. Food mixer is then stopped, bowl removed and foam cast into previously released room temperature molds by hand, pouring, tools or injection. Close molds and allow the wet foam to ‘gel’. When foam has gelled, forming a semi-solid yet easily deformed mass, molds are placed in oven for 2 or more hours at a temperature of up to 100°C - 212°F to cure (vulcanize). Cure time depends upon how thick foam and molds are. Once cured to a rubber, foam is carefully removed from cooled molds, washed in water, dried and ready for use. Record all component amounts, room temperature, mixer speeds and times, gel time, oven temperature, cure time and results for later reference.
FORMULAS: Each brand has a slightly different formula which should be followed for best results. McLaughlin was first to introduce an easy to calculate formula with Curing and Gelling Agents 10% and Foaming Agent 20% of the latex by weight. For soft foam popular in film work the McLaughlin formula for a single batch is: 150 grams Latex, 15 Grams Curing Agent, 30 grams Foaming Agent and 15 grams Gelling Agent. Using fluid measurement this translates as: Slightly over 1/2 cup Latex, 1 level teaspoon Curing Agent, 1 tablespoon Foaming Agent, 1 level teaspoon Gelling Agent. McLaughlin Foaming Agents contain plasticizers. Use more for softer foam, less for tougher foam. For durable puppet foam cut the Foaming Agent back by 1/3 (20 grams or 2/3 of a tablespoon) or even by 1/2 (15 grams or 1/2 a tablespoon). Batches can be scaled up or down proportionately. Do NOT mix measurements, use one or the other, weight OR volume.
OVEN Should be capable of evenly distributing heat throughout its heating chamber and should reach boiling point ... 212°F / 100°C. Fan assisted, convection ovens are popular. Micro waves don't work well. An accurate temperature reading is important and an oven thermometer is a wise investment for this purpose. If the oven is electric an inexpensive lighting timer (from Radio Shack / Tandys) will turn the oven off automatically. If you must use a domestic oven for baking foam: seal molds in heat proof plastic bags made for cooking poultry and thoroughly clean oven after use.
MIXER: The Sunbeam Mixmaster in the USA and Kenwood Chef in the UK are popular. You can sometimes find second hand mixers at garage sales and charity stores like the Salvation Army. A mixer for foam should be free standing (hand held models won't do), with a whisk or two (not a dough hook), and should be variable with at least high, medium and low speeds. Once used for foam do not use a household mixer for food. No two mixers run at the exact same speeds. Keep notes of how long and at which speeds you make your foam to develop a foam run schedule for your workshop and mixer.
AIR / LATEX RATIO, VOLUMES: Varies the softness and density of latex foam. The less air whipped into latex the denser / tougher cured and more pourable wet foam will be. The more air whipped into latex the lighter / softer cured and less pourable wet foam will be. Latex can be frothed up to volumes of more than 10 (9 parts air to 1 part latex mixture). For puppets a volume of 5 (4 parts air to 1 part latex) is usually sufficient. For Stop Motion Puppets foam volumes of 3 or 4 ought to do. Animatronics with delicate mechanisms may require higher volumes.
DE-AMMONIATION / GELLING: This is the part newbies mess up most. It is important to understand latex gellation and it’s relationship with ammonia for consistently successful foam making. Gellation makes latex foam possible in the first place by locking the fluid foam into the shape it was cast so it may be cured into a resilient natural rubber foam. Gelled latex will hold its shape but has no elastic memory until it is cured at temperatures up to boiling point at 212°F. If you stretch or squeeze uncured gelled latex foam it will not spring back and will stay permanently deformed. And un-gelled foam may collapse into a rubber blob when exposed to cure temperatures. This is why we wait for foam to gel before placing filled molds in an oven.
Ammonia is added to natural latex at the plantation as a preservative. By making an alkaline environment (high pH) ammonia serves two functions: 1) it keeps bacteria from attacking latex and 2) it prevents latex from coagulating. When the high pH of latex is reduced by removing ammonia it will coagulate forming a gel.
The Gelling Agent has a delayed action but it is not a miracle worker. The Gelling Agent will reduce the pH by only 1 pH point or so. The pH scale runs from 1 (highly Acid) through 7 (neutral) to 14 (highly Alkaline or Basic). To help the Gelling Agent do it's thing we reduce the pH of wet latex foam from a pH of about 10.5 to a pH of about 9 through deammoniation. Latex coagulates, gels, at a pH on the alkaline side of neutrality somewhere between pH 7 and pH 8.5 depending upon the latex and the foam formula.
The Refining Stage has two purposes: 1) to reduce the size of air cells and ensure they are of uniform size and 2) to drive off most (not all) of the ammonia. Foam’s air cells will usually be refined well before ammonia is driven off. If you don’t drive off most of the ammonia the foam may take a long time to Gel, if at all. If you drive off all the ammonia the foam will gel in the bowl and on your whisk. You want to smell a little ammonia when adding the Gelling Agent. Keep notes on temperature, humidity, frothing and refining / de-ammoniation times, mixer speeds and gel times to develop a formula for your workshop.
GEL TIME: The amount of time it takes wet latex foam to coagulate after gelling agent is added. Ideally you want to have enough time to fill and close molds before foam gels, 15 minutes or so is usually enough. Shorten gel times by increasing deammoniation time, lengthen gel times by decreasing deammoniation time. Long gel times of 1 hour or more can produce perfectly useable results, given that the foam has not collapsed.
ROOM TEMPERATURE: Gel times will be faster on warm days and slower on cool days. If possible, run foam in a warm room, between 70 - 75°F for most consistent results. Foam is not very successful in rooms under 65°F and may collapse in molds before gelling.
COLOR: Pure latex foam cures an off white color. Coloring is not essential, but when added at the same time, foam color helps show when the Gelling Agent is mixed in and is helpful for beginners. Pre colored foam will also help should it tear during a performance. There won't be a stark piece of white foam showing through the tear. Most brands do Foam Colors.
Do you want a GREAT foam coloring tip for puppets? Being a natural product, latex foam takes fabric dyes well. Don't use it to color wet foam in the bowl because it will upset gellation, big time. Rit, Dylon and all the rest can be used to dye CURED foam, once it is out of the mold, in any of the many colors available. Use it just like you would to dye a piece of cotton or silk.
SHRINKAGE: Latex Foam shrinks about 10% and is more pronounced in large, thick pieces. Scaling up your sculpture is the answer. Foam from molds that have been ‘Cored Out’ will shrink less and more evenly than solid foam castings. Foam made with high solids latex shrinks the least.
WASHING: Washing latex foam before use is a must, especially now with more people reporting being sensitive to latex proteins. It will greatly reduce foam’s sulfur smell and extend its life by removing excess curing chemicals. Simply soak foam in water for a few minutes, squeeze out and repeat with fresh water until water runs clear. Dry on cloth or paper towel, or on the mold core to help retain its shape. Foam shrinks least when allowed to dry slowly at room temperature.
MOLD CONSIDERATIONS: Molds for latex foam must withstand repeated heating and cooling. For proper registration, 'keys' on all mold sections are sculpted into clay dividing walls. Puppet molds are made in 2 parts (front and back) or 3 parts (front, back and core). Latex foam is flexible and will pull out of most mold undercuts. The parting line for a head mold can be placed down the sides of the head and neck, behind or down the middle of the ears where it is out of sight. If you already make plaster molds you will already have many skills needed for latex foam molds.
MOLD MATERIALS: Molds can be made of gypsum, fiber glass, epoxy, even flexible silicone and tough steel or aluminum. UltraCal 30 or Crystical R will do fine for most molds. These are strong gypsum (plaster) products made by US Gypsum and British Gypsum respectively. They are easy to work with, have low toxicity and are relatively inexpensive. A builder’s supply store may be able to order them for you. You could buy them mail order from sculpture or special effect stores, but they can be expensive to transport due to gypsum’s weight. Ordinary plaster of Paris will not last through several cure cycles. UltraCal and Crystical molds have been known to last 40 or more cure cycles. One inch thick gypsum molds are sufficient for most sized puppets.
GREEN MOLDS: A gypsum mold will harden before it has fully cured. Molds need to be fully cured and almost bone dry before foam will successfully gel and cure in them. It is a waste of time and materials casting foam into fresh molds. Drying can take a few of days at room temperature. This can be speeded up in an oven with heat set at about 100 - 150°F for 6 or more hours. Fresh molds are referred to as being ‘green’. Actually gray or off-white, dry gypsum molds take on a markedly lighter shade and will ‘ching’ rather than ‘clunk’ when tapped. Fiberglass, epoxy and silicone molds also need time to fully cure and exude residual catalyst before latex foam may be cast into them.
MOLD REINFORCEMENT: Reinforced gypsum molds last longer. It is best to laminate fibrous material into molds as they are made. If a mold falls or cools down too fast and cracks, the fibers will hold it together. Open weave burlap or hemp fibers are widely used. It’s a matter of preference and what is available. You don’t need both. Using dry burlap or hemp fibers can cause mold de-lamination where your mold literally comes apart in layers. It is important to wet both materials so they don’t dry out gypsum before it has hardened.
‘CORING OUT’ MOLD: This is where you sculpt the inside of what will be your foam. Solid hands and feet won’t need a core, but most puppet heads will. Solid puppet heads are heavy and cutting latex foam is more difficult than polyfoam. Carving out a latex foam head is not really an option unless you really have to. It’s best to allow for hand access by laying clay into a mold where you want foam then create a third mold part - the core. A core directs foam exactly where you want it to go, saving both weight and materials. Cut or roll water-based clay into 1/2 inch thick slabs, trim and lay into your mold halves. Use a toothpick, pin or pointed tool to poke into the clay to gauge uniformity of thickness, then smooth with the fingers or tool. You can even sculpt finger grips. When finished, close mold halves, put mold release on exposed gypsum and cast the core. For registration, a ‘locking’ shape is designed into the base of mold and core so they fit together properly. For puppets like talking books, paintings and bass reliefs where sculpting is relatively flat and one sided, a two piece mold will be sufficient with the back half acting as the core.
GLUE: The best glue for latex foam is one part Contact Cement. It is made of neoprene rubber and has an ochre yellow color. It glues latex foam to itself and many other puppet materials. It remains flexible when dry and is available in solvent and water based formulas from most D.I.Y., building supply, craft and art stores.
PAINT: Few ready made paints are flexible enough for latex foam. Acrylics will crack and flake off. Paint for foam puppets can be made with pre-vulcanized latex and acrylic paints. Thin for brushing or spraying with water containing several drops of ammonia. 1 part acrylic paint, 4 parts latex and 5 parts ammonia water is a good formula for spraying. Dip, rinse and keep brushes wet in ammonia water as you paint and immediately wash in ammonia water with detergent when finished. Use only enough latex paint to color foam’s surface and don’t get into cells as it will stick when dry. Powder dried latex paint to prevent it sticking to itself. Paints keep for several weeks in airtight containers. Alcohol activated Temporary Tattoo Makeup can be used (Reel Tattoo Colors / Skin Illustrator / Kryolan / Michael Davy brands from Theatrical Makeup Stores) and the Monster Makers do a ready made Latex Paint suitable for spraying. Other paints for latex foam are home made and exceed the scope of this article. Get the book when it’s ready. (Plug, plug.)
LIGHT: Exposure to strong light will rapidly degrade latex. Ultra violet (UV) rays cause the deterioration. Performing outdoors in full sunlight or in environments lit with black (UV) light will shorten the life span of latex puppets.
FATS AND OILS: Animal, vegetable or petroleum fats and oils will plasticize foam and turn it gooey. Entertainers at restaurants and parties want to avoid children with greasy hands fondling their puppets.
COPPER: Copper and its alloys seriously degrade and rapidly discolor latex. It’s like Superman and Kryptonite. They were just not meant to go together. Copper first turns foam green, then brown and eventually black. Pigments and metals containing copper are to be avoided and alternatives used instead. Copper from pennies in a pocket full of coins and paper money transferred to your hand is enough to rot the inside of a puppet’s mouth. Sweat from your hand will speed up the process. Freshly demolded foam pieces will immediately discolor and will forever sport brown fingerprints. Wash hands before touching foam to play it safe. If you must use copper directly against latex foam for animation mechanics, coating the metal with automotive lacquer or nail polish helps as a barrier.
CLEANING: Clean soiled latex foam as soon as possible to prevent staining with a cloth wet with water or isopropyl alcohol. Stronger solvents may damage the foam, paint or both. If a stain is bad, touch up or repainting may be required.
STORAGE & LIFE EXPECTANCY: Foam chemicals stored tightly capped in a cool room will last a year or more. Shake them every month or so. Cured latex stored in plastic bags in a dry place away from light can last 20 years or more. Place puppets in a plastic bag in a box somewhere safe. Don’t squash puppets as they may stay deformed. Give them some breathing space. Stuff paper or cloth into heads to keep their shape when stored for long periods. Latex foam I formulated for the Tarzan movie Greystoke kept in sealed plastic bags was reported to be as subtle as new more than 15 years after its manufacture. With Miss Piggy being used every day of the week on the original Muppet Show it was common to replace her every 6 - 12 months. Mouth corners and necks are the first to go on latex foam puppets. Performing on weekends and holidays, a latex foam puppet could last many years. It’s wise to have a backup puppet in case of an accident when doing film and television work.
NO MOLDS - LATEX FOAM ON POLYURETHANE FOAM: A fun technique is applying wet latex foam to carved polyurethane foam. Cured, it provides a surface skin to the polyfoam. Gelled foam can be textured and sculpted (somewhat) with tools and texture stamps. More latex foam may be added to previously gelled foam. A terry cloth towel or bristle brush may be pressed into gelled foam to simulate skin pores. All the Pod People in Jim Henson’s The Dark Crystal movie were made this way. Not one single mold was required to make the heads, hands and feet of these characters. Without having to get heat through a mold, puppets made this way cure faster. Cure for one hour or more.
HEALTH, SAFETY, ALLERGIES, DISCLAIMER: Be thoroughly familiar with health and safety information found in Manufacturer’s Safety Data Sheets (MSDS) and instructions. Keep rubber chemicals safely away from children. Do not use foam containers, mixer or utensils for food. Wear protective gloves and clothing when handling chemicals and making foam. Wash hands before eating, drinking or smoking. With allergies to latex proteins becoming prevalent washing foam before use is more important than ever. While a small percentage of the population report latex allergies, thousands of rubber plantation, factory and special effect workers handle latex on a daily basis with no adverse reactions. Some people’s immune systems may be more sensitive than others. Your health and safety is your responsibility. If latex makes you feel ill do not use it. The information here is presented in good faith but use at your own risk. The author and publisher assume no responsibility for your actions and safety regardless of the legal theory advanced.
Tom McLaughlin has been making rubber puppets since he was a kid. He studied sculpture at New York’s School of Visual Arts and rubber technology with Akron University. Tom has formulated rubbers for the Muppets, Bil Baird, Disney and others. Puppets Tom has made in rubber include Miss Piggy, Statler, Waldorf, Yoda, Jabba the Hut, the cast of The Dark Crystal and Babe. His ultra realistic silicone skins for Babe helped win it an Academy Award for Best Visual Effects. He speaks and gives workshops on creative applications of rubber, is author of Silicone Art, composes music, and continues to consult for films, television and industry.
A NOTE FROM THE AUTHOR: What started out as a short essay is turning into a book. This is good. I have wanted to do a book on latex foam puppets for many years. Information presented here is a general overview to hopefully inspire and get you started. (Quick, get into advertising and save the world from the current barrage of second rate computer animation! Please.)
The book will contain tips, tricks, formulas and stories gathered over a lifetime of special effect rubber work and will include full instructions for a new latex foam paint system I'm developing. If you have any historical info on rubber puppets or photographs for the book please do contact me, as should any interested publishers.
If you didn't know, in the 1980's my foamed latex formula was stolen and hundreds of productions have since used it without any benefit to me. It broke my spirit for many years. The Monster Makers now make my formula under license in the USA. While I hope you will consider trying my formula, any of the latx foams listed on the internet will work for puppets.
McLaughlin Foam - Special effect and mask supply store Monster Makers offer the author's original Animatronic formula for puppets and Prosthetic formula for makeup appliances. Marketed in the USA as Monster Makers Foam, McLaughlin Foam is now sold worldwide through Kryolan makeup distributors. Monster Makers do start up kits for beginners with everything needed to make latex foam puppets. Does custom foam casting and molding work. Great source of puppet making supplies. order their new catalog ... or download it via their website. Monster Makers, Cleveland, Ohio, USA. www.monstermakers.com www.mclaughlinfoam.com
©2002 Tom McLaughlin