Insulation mattress size logic

What is logic behind size of insulation mattress which is

50 x 1220 x 1640 mm LRB or

50 x 3810 x 610 mm ceramic wool

 

We already know that IS 8183:1993 does not insist for specific size.

further 1220 x 1640 mm = 2 sq meter area

1220 mm = 4 ft ( interesting ? )

but still it seems that there a logic behind that