Insulate a trap door that swings down on a hinge

Get an airtight insulated attic hatch.

e.g.

https://www.ecologicalbuildingsystems.com/products/airtight-windtight-systems/attic-hatches

I think you need a two surfaces pressing together with a compressible draft excluder strip fitted to one of them.

You could do this by adding a lip above the door, but the detailing is important and you're going to have to design it yourself. Difficult to recommend an approach without knowing how handy you are and what tools you have.

My attic opening already had a reasonable rubber seal around the opening for airtightness but when I added 175mm of insulation to the attic floor, I started to get a small condensation problem directly above the hatch. Figuring this was due to heat rising through the hatch into the now cooler attic space, I just cut out a tight-fitting sheet of that reflective bubble-wrap which fits snugly into the higher-walled opening (as a result of the additional insulation height) and the condensation problem disappeared immediately. So very cheap solution but evidently quite effective too.

Exactly what I'd come here to suggest but it might be easier to handle if the insulation was put in a really large plastic bag. You could also use an old single duvet cover. The edges of the bag could be weighted if a better seal was required.

that is what I did, but my hatch pushes upwards.

for the drop down type they could cut it back at an angle. but 100mm probably to thick for what they have

the tent (or the insulation in a duvet cover) is the best solution in this case I think

I can think of plenty of solutions but the problem is they won't work with the ladder up. You need the ladder down to fit any insulation in place. If you want to get out a pair of step ladders then just cut a piece of 50mm (or thicker) kingspan so it fits the hole and is held in by the casing. Easy enough to poke the insulation out of the way to get the ladders down but would need the step ladders to refit it.

Just go with draft excluder seal then where the door closes . Get down to your local lidl I seen they have them in again atm

https://www.screwfix.ie/p/stormguard-sureseal-3-self-adhesive-foam-draught-excluder-weatherstrips-black-7-5m-2-pack/493VV?gad_source=1&gclid=EAIaIQobChMI4MTZgdmsiQMVqIlQBh2ZcRi_EAQYAiABEgKl2_D_BwE&gclsrc=aw.ds

Yea you have to bed them in so spend some time rolling them down and pushing the door up and holding it so they flatten down but they will as they are a foam material

It does not but it stops the gap around the door he mentioned, where a draft could possibly be coming in.

Keep it simple. Make a fibreglass insulation filled polythene bag "cushion", at least a 100mm wider and 100mm longer than the opening. You will need to use a step ladder or chair to place the cushion into position across the opening before closing the trap. Added benefit of this is that several years down the line, when you may have to open the hatch for access, all the loft debris, dead insects and dirt will be on top of the cushion and will not fall on your head when you open the hatch. Simply slide the cushion across and there you have it. Simple.