All growing environments need the right ventilation because too much warmth and humidity can be just as damaging as too little.
Aluminium or Treated Timber is clamped around the outside of the polytunnel framework at approximately 3ft from ground level. Ventilation net of 50% shade is then placed from this rail to the ground and either trenched or attached to base rails (if ordered).
A polythene blind can also be added which screens off the Side Ventilation net when required. This gives you the option of full or partial ventilation. A simple gear mechanism lowers the screen from the side timber rail allowing ventilation of plant foliage whilst still protecting root systems from wind chill.
Please note, the vent screen blind cannot be used in conjunction with aluminium side vent and aluminium base rails
Tube problem 
Protect your crops as early winter sets a November record! 
Picking Polythene for your Polytunnel