Film coating seeds uses a thin polymer film to cover the seed. Film coating only adds 1 to 5 percent to the weight of a seed compared to over 1,000 percent for pelletizied seed.
It has become common for treated seeds to be coated with colorful films. This indicates that the seed has been treated so it will not be used as a food stuff.
A rotary film coater used to coat small seeds.
The film coating is added as the seeds spin to insure even coating.
The most common reason to film coat field grown crops is to use the film as a carrier for pesticides. It is very common to see sweet corn coated with a film that contains a fungicide.
This aides in seedling stand establishment especially for early season sowing where the soil temperature is low and seedling emergence is delayed.