Thermoforming process that is after heating the plastic sheet  in the oven,the plastic will become soften.With the female or male mold(usually it is alumunium mold),to get an airtight space surrouding and sucking air in the cavity,the plastic sheet will be prssed in the mold surface to be heated and vacuum formed to the products. 

Thermoforming process:                                                                                                                                      Step 1:    Heating plastic sheet   
Step 2:   Vacuum forming to shape
Step 3:   Cooling to maintain shape
Step 4:    Making  half finished product
Step 5:   CNC Processing
Step 6:   Trimming edges
Step 7:   Drilling holes
Step 8:   Examination and checking
Step 9:   Cleaning and Packaging

Thermoforming plastic option:

ABS-acrylonitrile-butadiene-styrene

PS/HIPS-polystyrene/high impact polystyrene

PMMA-acrylic

PET/PETG-polyethylene terephthalate/polyethylene glycol terephthalate

HDPE-high-density polyethylene

PC-polycarbonates

PVC-polyvinyl chloride