Based on the position/opening of the mouth, what type of vowels are इ, ई, उ, ऊ (i, ee, u, oo)?

Based on the degree of opening of the mouth canal during pronunciation, vowels are categorized into Samvrit, Ardha-Samvrit, Vivrit, and Ardha-Vivrit. 'Samvrit' (Close) vowels are those during whose pronunciation the mouth is almost closed. These include इ, ई, उ, ऊ.