A curable composition comprising: i) a glycidyl ether of a novolac, comprising or consisting of moieties having the formula (I), wherein —Ra is either always hydrogen or always methyl; —B is either always *—CH2-** or always formula (A); —a fraction of 0.8 to 0.99 of the Y moieties are essentially —O-glycidyl, this fraction being designated as x, and the remainder of the Y moieties, this fraction being designated as (1-x), are divalent bridging spacers of the structure *—O—CH2—CH(OH)—CH2—O—** connecting two moieties according to above formula (I); and—n is a number in the range of 0.1 to 3.0; and wherein said novolac glycidyl ether has an epoxy equivalent weight FEW in the range of 160 to 270 g/eq. and the average number of epoxy groups per molecule of novolac glycidyl ether (I), designated as f, is in the range of 2.1 to 5.0; ii) dicyandiamide; and iii) an urea derivative of the formula (II). This composition is stable upon storage at room temperature and fire-retardant. It can be used for preparation of prepregs and in core filling, particularly in the aerospace field.