Describes a polymerizable composition of (a) a first allyl functional monomer, which is selected such that a substantially completely cured polymerizate of the first allyl functional monomer has a 15 second Barcol 934 hardness of at least 40, and (b) a second allyl functional monomer selected from polyether diol bis(allyl carbonate), polylactone diol bis(allyl carbonate) and mixtures thereof. The second allyl functional monomer is present in the composition in an amount to provide a substantially completely cured polymerizate having: (i) improved organic photochromic substance incorporation relative to a substantially completely cured polymerizate of the composition free of monomer (b); and (ii) heat distortion temperature of at least 40° C.