I’m not quite sure what you mean – the bags are just that – bags meaning one end is already sealed – OTOH maybe you meant to seal one end and then cut the other end open and seal from the other direction. I would NOT do that. What you want to do is to massage as much air out of the bag as you can before starting the sealing process – that will help greatly. There are several other tricks posted elsewhere – one is to even take a soda straw and carefully suck air out of the bag after massaging it. Or the trick of submersing the air into a vessel of water which will push air out as well.