Plastic Netting is necessary to allow the air to flow out from around your pressing. Without it, when starting to pump air out of your vacuum bag, the vinyl might suction down only in the spot right under the valve and may not evacuate the air from the whole bag.
By placing this under the valve and across your project, it creates a pathway for the air to reach the valve.
What else can I use if I can't find my Breather Netting
Use any similar net-like material, as long as it will not adhere to your project if any glue seeps onto it during the process of laminating.
Can I cut this?
Yes, you only need enough to cover a portion of your project. Use scissors.
4' (120 cm) length of breather netting