Pop-hole doors from Tulderhof are solid, draught free and can me made in many different sizes.
The pop-hole doors have a special insulated foam at the wall side of the slide. This foam has an outside rubber layer which prevents the hens from pecking this foam.
The pop-hole door closes draught free because of the special closing mechanism invented by Tulderhof (see fig. below). When the slide is moving downwards it gets pushed against the wall and closes hermetically.