machine applying stretch film
   Source: Taarup

To make good quality silage it is important that good quality materials and equipment are used and clearly that includes the bale wrap film. Stretch film bale wrap should meet several key requirements:

  • Consistent quality and thickness
  • Good stretch properties even in warm weather
  • No tendency of “windowing” when being stretched
  • Good cling between layers
  • Puncture resistance
  • Retention of strength over many months in the open
  • Impermeability to air and moisture

A quality film brings benefits for contractors and farmers during the bale wrapping process because there are fewer stoppages resulting from tears, inconsistent stretch or jamming of the equipment.

Importance of quality

The quality of the stretch film used must be high due to the demands placed on the material during wrapping, transport and storage:

  • Maintain the bale density and integrity over a prolonged period in widely varying climatic conditions and withstand typical handling.
  • Reflect heat from the sun — preventing increased temperatures that lead to the growth of undesirable microbes and increases in gas permeation through the stretch film.
  • Present a water and oxygen barrier and keep the carbon dioxide gas inside the bale as a preservation agent.

Film requirements

The plastic film has a vital role in producing good bale silage. The film must withstand the tension required to achieve a tightly wrapped bale and retain its strength for at least a year while exposed to the environment. Pre-stretching of film means it can be wrapped tightly around the bale and will remain tight. It should also have surface tackiness to hold the wrap in place, impermeability to water and the lowest attainable permeability to oxygen. Multiple layers of film increase the barrier effects.

Film colour

Film is available in a choice of colours. The usual options are white, black and light or dark green. Black and green are the most popular in Central and South European countries, with usage varying between countries. White film is very popular in Northern European countries.

Although the pigments used mean green films have a small price premium, they are increasing in popularity because of their ability to blend into the landscape, and they avoid the high temperatures generated inside black bales exposed to strong sunlight. Heating leads to loss of nutritional value and potentially to spoilage in the conserved silage.

Film width

Film is supplied on rolls in widths of 500, 750 or 1000 mm. The most frequently used width in most European countries is 750 mm, which offers benefits of speed and more effective sealing of the bales.

Quality labels

In some European countries good quality bale wrap carry a national ‘quality mark’, like the ‘NF’ mark in France or the ‘SP’ mark in Sweden. These quality labels are issued by independent national testing institutes to guarantee customers benefit from high film quality standards. These include ultra-violet resistance, resistance to perforation, adhesion and dimensional properties such as stretch (55 – 70%) with even thickness. The specified properties ensure the film performs well in wrapping process and in protecting and conserving the forage.