In this link three possibilities are laid out for Jesus' flesh to be either;
1) His flesh typifies the veil (traditional view),
2) The new and living way through the veil with the emphasis being on his flesh as the way through (supported by Westcott)
3) Lane suggests that his flesh refers back to the entirety of the preceding statement, i.e. the free access we have through his blood making a new way through the veil.
Drs. Decker and Slusser maintain that option 2 is made impossible by an idiomatic rule of Greek grammer regarding the phrase τοῦτ᾿ ἔστιν:
"whenever there is an explicit antecedent (i.e., there is a specific word that serves as the antecedent; some occurrences of the phrase τοῦτ᾿ ἔστιν have a general antecedent in which some phrase or concept serves as the antecedent rather than a specific word), the word following τοῦτ᾿ ἔστιν always agrees with its antecedent in case and almost always in gender and number.† When the two words are both nouns, agreement in gender is not always possible since nouns have fixed gender; when one of the words is a pronoun, adjective, or participle, they usually agree in gender.§"
They regard the traditional view as most likely because of the proximity of an explicit antecedent agreeing in case, gender, and number but allow that Lanes supposition of a general antecedent is not ruled out and is thematically consistent with the larger context.