Question

in winter is it good to cover with 1thickest blanket or 2 or more lean blankets

Answer 1

I think it is better to cover 2 or more lean blankets because the air  between the  lean blankets act as insulators and keep the body warm

Answer 2

2 thin blankets would be better as the air between them will act as a poor conductor of heat, air will also not escape thus keeping you warm.