Lining Shed with MDF

[Luton Pete]

Two questions on my Shed insulating and lining. I have installed the xtratherm already with 60mm on walls and 75mm on ceiling. Do I need a plastic sheet or membrane as well before i put MDF boards up or not, I have sealed the joinsa nd everything with the foil tape. Most ive seen online havent done that but i saw one that did and it got me worried, The Insulation boards are foil backed Xtratherm ones

Second question when I,m lining interior over the insulation boards with moisture retardant MDF , do I put boards on ceiling first or the walls?

Thanks

 

[blup]

If the purpose of the foil is for insulation, should it not face in. A vapour barrier would be on the inside.

Blup

 

[foxhole]

I would not recommend mdf in shed even moisture resistant .
Osb is more suitable ( and cheaper)
What is the heat source?