Sol-gel fractions have been measured for cotton celluloses crosslinked with formaldehyde under widely different conditions of reaction and have been employed for estimation of the efficiency of crosslinking in the various processes. Most efficient utilization of formaldehyde for insolubilization of molecular chains is indicated for an aqueous process (form W′) and least efficient utilization is indicated for a nonaqueous process (form D′), the difference in efficiency being approximately a factor of 40. Interpretation of sol-gel data has been made relative to a model assuming random reaction of crosslinking agent throughout the cotton cellulose and by relationships developed by Charlesby and Pinner and by Shultz. This leads to estimates of relative numbers (moles) of effective chain elements per gram, ve (i.e., twice the number of effective crosslinks), which decrease in the following sequence for cottons at the 0.20% level of formaldehyde (i.e., 6.7 × 10−5 mole/g.): aqueous process, higher formaldehyde concentration (W′, ve = 4.8 × 10−5), vapor process (V, ve = 1.75 × 10−5), bake-cure process (C, ve = 1.37 × 10−5), aqueous process, lower formaldehyde concentration (W, ve = 0.95 × 10−5), nonaqueous process (D, ve = 0.03 × 10−5).