How to Make Waterproof Fabric with Liquid Latex

Purchase liquid latex. There are many brands and varieties available, but they generally fall into two categories: latex for theater prosthetics, and latex designed for spreading over one's body to create customized "suits." The latter type is preferable for this project, as it spreads more evenly and comes in a wider variety of colors which you can match to your fabric (costume latex generally comes in peach). If using a stretchy fabric, bear in mind that applying latex to it will hold it in whatever stretched position you have it in during application, to some extent (latex is stretchy, but less stretchy than most knit fabrics).

Turn your fabric upside down on your work station. If you are waterproofing a garment, first wrap your dressmaking dummy, mannequin or volunteer with plastic wrap secured with tape, then turn the garment inside out before placing it on. This will prevent the latex from sticking to the dummy or your volunteer if it seeps through the garment.

Spread the latex carefully over the inside/backside of the fabric using a paintbrush (this brush will be unusable after), or sponge. Bear in mind that some seepage of latex onto the other side of the fabric is unavoidable, especially with thinner materials. Spreading the latex more thinly can help avoid this problem, but you may find that your fabric is less watertight as a result.

Dry the latex with a hairdryer if using a volunteer (for the sake of speed). Otherwise, allow it to air-dry. The latex is dry when you can no longer move it with your finger, though it will remain slightly sticky for a while. If you wish to combat this, use talcum powder or cornstarch.