5 Tips to Create the Perfect Positive Mould for Prosthetics

Forming a socket, whether it is a check or flexible socket, always starts with a positive mould. This positive mould can be made of plaster or foam, but in general, both materials are shaped and adjusted in a very similar way.

If you consider the following tips and tricks when making and positioning a positive mould, you will reach the best results for your final socket. An added benefit of this method is that you will not have to use a tricot cover.


Tip 1: Position the positive mould on a round pipe or metal rod that is vertically aligned

Make sure to give the positive mould a broad and conical base. A good foundation will give you the advantage of easily forming and removing the final socket.

The edge of the positive mould should be longer than the proximal edge of the final socket. This will allow you to easily mould the edges of the socket. The proximal edge should be about 5 cm (2″) long.


Tip 2: Polish/Buff the positive mould

The plaster or foam must have a smooth surface, so the socket will have a smooth surface on the inside. All imperfections on the mould will be transferred to the check socket. Use regular and waterproof sandpaper with a P1000 to P1500 grit.


Tip 3: Make air extraction ducts in the positive mould

Give your positive mould air extraction ducts underneath the proximal borders of the socket, so that the vacuum suction can do its work.


Tip 4 (when making a plaster positive mould): Apply an acrylic varnish to the plaster

Keep in mind that water is enemy number one of high-temperature thermoplastic sheet materials. If water comes in contact with the thermoplastic, the final socket will have an uneven, milky surface and air bubbles. Take this into account when making a plaster positive mould. This issue does not occur with foam positive moulds.

To prevent water from interacting with the high-temperature thermoplastic, you can isolate the mould with an acrylic varnish.


Tip 5: Apply a silicone demoulding spray

As a final step to prepare your positive mould before positioning it, you can apply a light layer of silicone demoulding spray. This silicone layer will ensure that the material does not stick to the positive mould during application and that it will easily come off once it has cooled down.


Written by Marc Blij

Marc studied in Brussels and London and is a certified Orthotist and Prosthetist.

After working in an O&P lab at the Universities of Louvain and Brussels, he decided to set up his own O&P lab in Antwerp. For over 30 years, he ran his own practice, together with his wife.

Since 2006, Marc works at the Orfit Industries headquarters in Wijnegem (Belgium) as a Product and Educational Specialist in Orthotics & Prosthetics and Physical Rehabilitation.


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