In our silver anniversary episode, Phil and Eric talk about the lexical set dress, and all the various vowels that are associated with it. That includes [e] or is it [ɛ]? The guys try to uncover the history behind the choice to use [e], and advocate pretty hard for their preference, [ɛ]. Show Notes: We referred to these as we chatted, but wandered all over the place, so we probably don’t get to most of them... DRESS Open-mid front unrounded vowel Notice that it isn’t mid. We don’t have a symbol there at mid. It’s front , though we can feel how much more front /i/ is. The chart reflects this It’s unrounded, but that doesn’t necessarily mean spread. It’s a short vowel It’s a checked vowel Cardinal vowel #3 – Daniel Jones /ɛ/ Cardinal vowel #2 – Daniel Jones /e/ “Cardinal vowels (2), (3), and (4) are defined as front vowels that form a series of auditorily equidistant steps between cardinal vowels (1) and (5)” -Ladefoged Jones also makes a tense/lax distinction In The Pronunciation of English: We distinguish two intermediate positions, half-closed and half-open, in which the tongue is lowered from the closed position to about one-third, and two-thirds, of the total distance from the closed position to the open position Examples of …, halfclosed, half-open, … vowels are e (pen, pen), ɛ (pair, pɛə), e: the half-closed front tense unrounded vowel ɛ: a lengthened ɛ e Half-closed front lax unrounded. Examples: pen, pen, head, hed. 
In L this vowel is often replaced by i, e.g. git, indʒin for get (get), endʒin (engine). In many dialects it is replaced by the opener ɛ , thus, pɛn, hɛd.

Besides occurring independently, the sound e occurs in StP as the first element of the diphthong ei, e.g. day, dei. With many speakers, especially in N.Eng. this diphthong is tense, i.e. the two elements are the tense vowels corresponding to the lax e, i. In Sc the diphthong is not generally used, a pure tense vowel (phonetic symbol e:) being substituted (de:). In L the first element of the diphthong ei is much opener than in StP, becoming ɛ, æ, a, or even ɑ, thus dɛi, dæi, dai, dɑi. In L e sometimes occurs instead of ʌ 

Note the faulty pronunciation of aerate (StP eiəreit or eəreit) as ɛəreit or iəreit. The words again, always are often pronounced agen, ɔ:lwiz, ɔ:lwəz, but the forms agein, ɔ:lweiz are preferable.

Half-open front unrounded. This sound only occurs in StP in the diphthong ɛə. Examples there, their, ðɛə. See also the previous section. In the pronunciation of many S.Eng. speakers, the first element of this diphthong is more open than ɛ, being in fact practically æ (ðæə). The form ɛə is preferable. In L the first element of this diphthong is the half-closed tense vowel e: (ðeə) “The standard lexical set DRESS is defined as comprising those words whose citation form in RP has the stressed vowel /e/ and in GenAm /ɛ/” -Wells step, bet, neck, fetch, Jeff, mess, mesh, ebb, bed, egg, edge, rev, fez, hem, pen, bell, shelf, hemp, tent, theft, best, sex, next, effort, method, terror, tenor, jelly, centre/center, pester, threat, sweat, deaf, death, bread, dead, head, health, realm, meant, breast, ready, jealous, pleasant, weather, treacherous