warped film!

I just had 3 rolls of Portra 400NC processed at a lab I'm familiar with. The film came back badly warped. Not curled as is more often the case. Each individual negative is warped and wavy. The film was uncut and sleeved when it came back to me, as I requested. It's impossible to keep flat in a glassless carrier and even one side glass does not help much. With glass top and bottom the problem is almost completely resolved. I've only used 120 in the past. I'm wondering if this is something peculiar to 220 or did something go wrong at the lab. What do you think???

Put them between books for a week. Books that are too heavy to read are good for this purpose .

Get the bathroom hot and steamy then tie a nylon fishing line across the shower and hand the film with weights [see FreeStyle Arista Stainless Steel Film Clips Set of 2 Model# 66361] at the end until the film is dry.

Steve