How to Cast Your Own Silicone Breast Forms

Casting your own silicone breast forms gives you complete control over size, shape, weight, skin tone matching, and surface texture. It's an advanced technique requiring patience and practice, but the results — custom forms perfectly matched to your costume, body, and character requirements — are impossible to achieve any other way.

Materials and Safety for Silicone Casting

Platinum-cure silicone is the only appropriate material for body-contact silicone forms. Specifically, choose a Shore A hardness between 10 and 20 for wearable forms — soft enough to move naturally, firm enough to hold shape. Smooth-On's EcoFlex 00-30 and Dragon Skin 10 are widely used in the prosthetics community for exactly this application. Never use hardware store silicone caulk, which contains acetic acid and is not body-safe.

Silicone-compatible pigments (not acrylic paint, which will not cure properly in silicone) are used to color forms. Silc-Pig from Smooth-On is the most widely available and comes in skin tone ranges as well as bright fantasy colors. Use sparingly — silicone pigment is concentrated and even a few drops tint a large batch.

Work in a well-ventilated space. Silicone off-gases during cure and while the cured material is generally non-toxic, working with large volumes in an enclosed space is unpleasant. Wear nitrile gloves — silicone is difficult to remove from skin and your fingerprints will transfer to any uncured surface.

Demonstrated by Chimera Costumes — How to Cast Your Own Silicone Breast Forms

Sculpting and Mold Making

Your sculpt is the master from which all casts are made. For breast forms, sculpt in oil-based clay (Roma Plastilina, Monster Clay, or Chavant NSP) over a rigid armature. Avoid sulfur-containing clays like natural sulfur-free clays if using platinum silicone — sulfur inhibits platinum cure. The sculpt should be smooth, symmetrical (or intentionally asymmetrical to match a specific body), and refined to the exact surface texture you want in the finished form.

Create a two-part mold from the sculpt using Ultracal 30 or a pourable urethane mold rubber. The two-part design allows you to demold the finished cast without destroying the mold, enabling multiple pulls. Register keys (interlocking bumps and divots) between mold halves keep alignment precise. Seal plaster molds with Vaseline or mold release before pouring silicone — unsealed plaster will bond to silicone and destroy both the mold and the cast.

Demonstrated by Chimera Costumes — How to Cast Your Own Silicone Breast Forms

Pouring, Curing, and Finishing

Mix your silicone components according to manufacturer ratio (typically 1:1 by weight) and add pigment to Part A before combining. Mix thoroughly for at least three minutes, scraping sides and bottom of the container. Under-mixed silicone will have uncured patches that remain tacky permanently. Vacuum degassing removes air bubbles — if you don't have a vacuum chamber, pour in a thin stream from height and rotate the mold while pouring to minimize trapping air.

Cure time varies: EcoFlex 00-30 demolds in about four hours at room temperature; Dragon Skin 10 takes longer. Cure at room temperature rather than accelerating with heat — heat curing can create surface defects. Once demolded, trim flash (thin silicone fins along the mold seam) with sharp scissors and blend the seam with a small amount of fresh uncured silicone.

Surface painting adds realism: thin silicone mixed with Silc-Pig, applied with a brush in thin translucent layers, creates the depth and color variation of natural skin tone. Veining can be painted on with a fine brush before applying a sealing coat of thinned silicone. Powder (cosmetic-grade translucent powder) removes surface tack and gives the finished form a skin-like matte finish.

Demonstrated by Chimera Costumes — How to Cast Your Own Silicone Breast Forms