It took a while for us to figure this one out, but Clip-n-Seals shipped in the belly of planes in the Winter, arrive partially frozen on our customers doorstep and they’re stiff. We make Clip-n-Seals with LDPE and that is affected by temperature. In the Winter, we suggest letting them warm up a bit before trying them out. The clamp should have a strong grip, but not require too much strength to close.