Interpret coefficients:

Call: lm$($formula $=$ pd ~ $1+$ moisture $+$ material $+$ moisture:material, data $=$ clay$)$ Residuals: Min $1$Q Median $3$Q Max $-8\mathrm{.}2343-2\mathrm{.}9072-0\mathrm{.}41212\mathrm{.}64267\mathrm{.}8457$ Coefficients: Estimate Std$.$ Error t value $($Intercept$)-103\mathrm{.}166611\mathrm{.}6696-8\mathrm{.}841$ moisture $7\mathrm{.}79280\mathrm{.}745410\mathrm{.}455$ materialplastic clay $23\mathrm{.}955713\mathrm{.}29861\mathrm{.}801$ materialsandy clay $29\mathrm{.}202917\mathrm{.}74931\mathrm{.}645$ moisture:materialplastic clay $-3\mathrm{.}59500\mathrm{.}7907-4\mathrm{.}547$ moisture:materialsandy clay $-3\mathrm{.}50360\mathrm{.}9388-3\mathrm{.}732$ Pr$(>|$t$|)($Intercept$)1\mathrm{.}07$e$-12***$ moisture $1\mathrm{.}77$e$-15***$ materialplastic clay $0\mathrm{.}076355.$ materialsandy clay $0\mathrm{.}104810$ moisture:materialplastic clay $2\mathrm{.}48$e$-05***$ moisture:materialsandy clay $0\mathrm{.}000406***---$ Signif. codes: $0***0\mathrm{.}001**0\mathrm{.}01*0\mathrm{.}05.0\mathrm{.}11$ Residual standard error: $4\mathrm{.}122$ on $64$ degrees of freedom Multiple R$-$squared: $0\mathrm{.}8776,$ Adjusted R$-$squared: $0\mathrm{.}868$ F$-$statistic: $91\mathrm{.}77$ on $5$ and $64$ DF$,$ p$-$value: $<2\mathrm{.}2$e$-16$