The Vac-u-form was a toy by Mattel made around 1961 with the trademark filed on October 8, 1962.
Based on the industrial process of vacuum forming, a rectangular piece of plastic was clamped in a holder and heated over a metal plate. When the plastic was soft, the holder was swung to the other side, over a mold of the object to be formed. Then quickly and repeatedly pressing down on a spring-loaded handle on the side of the unit created a vacuum, sucking the plastic down over the mold and shaping it to it. When the plastic cooled it solidified, making an impression of the item.
Various molds came with the kit. Several expansion kits were also available for molding various other shapes. In actual use almost any small object that could withstand the temperature of the heated plastic sheet for a few seconds could be used as a mold. Plastic refill sheets came in a variety of colors.
Mattel's VAC-U-FORM toy is well made and many are still in use today both as a toy and for small size part production in conjunction with other hobbies such as making R/C aircraft cowling and other parts.
Because very hot surfaces were easily accessible to a child (or adult) playing with the toy, it probably could not be sold today due to safety restrictions.