Manta vs. cobija vs. frazada
The Spanish words 'manta', 'cobija', and 'frazada' all refer to a blanket, but they are used differently depending on the regional dialects of Spanish-speaking countries.
Manta
In general, 'manta' is a broad term for any type of blanket. It is mostly used in Spain.
Hace frío, necesito una manta.
(It's cold, I need a blanket.)
Esta manta es muy suave y cálida.
(This blanket is very soft and warm.)
Cobija
'Cobija' is commonly used in Mexico and some parts of Central America and refers to a thicker, often quilted blanket.
Estoy buscando una cobija porque mi habitación es muy fría en la noche.
(I'm looking for a blanket because my room is very cold at night.)
La abuela me tejio esta cobija bonita.
(Grandma knitted this beautiful blanket for me.)
Frazada
'Frazada' is frequently used in South America such as Chile or Argentina. It usually refers to a heavy or woolen blanket.
Voy a traer una frazada porque la noche está muy fría.
(I'm going to bring a blanket because the night is very cold.)
La frazada que tengo en mi cama es muy pesada y calienta mucho.
(The blanket I have on my bed is very heavy and heats up a lot.)
Summary
'Manta', 'cobija', and 'frazada' all refer to a type of cover commonly known as 'blanket'. However, the usage depends upon regional dialects and variety of Spanish spoken. While 'manta' is used universally across Spanish speaking countries, 'cobija' finds particular use in Mexico and Central America and 'frazada' in South America. The slight differences also reflect the nature of the fabrics used locally.